diff --git a/data/abilities.ts b/data/abilities.ts
index 6cafbc88a6d3..d0fc33e2f4a6 100644
--- a/data/abilities.ts
+++ b/data/abilities.ts
@@ -1167,7 +1167,7 @@ export const Abilities: import('../sim/dex-abilities').AbilityDataTable = {
 	},
 	embodyaspectcornerstone: {
 		onStart(pokemon) {
-			if (pokemon.baseSpecies.name === 'Ogerpon-Cornerstone-Tera' &&
+			if (pokemon.baseSpecies.name === 'Ogerpon-Cornerstone-Tera' && pokemon.terastallized &&
 				this.effectState.embodied !== pokemon.previouslySwitchedIn) {
 				this.effectState.embodied = pokemon.previouslySwitchedIn;
 				this.boost({def: 1}, pokemon);
@@ -1180,7 +1180,7 @@ export const Abilities: import('../sim/dex-abilities').AbilityDataTable = {
 	},
 	embodyaspecthearthflame: {
 		onStart(pokemon) {
-			if (pokemon.baseSpecies.name === 'Ogerpon-Hearthflame-Tera' &&
+			if (pokemon.baseSpecies.name === 'Ogerpon-Hearthflame-Tera' && pokemon.terastallized &&
 				this.effectState.embodied !== pokemon.previouslySwitchedIn) {
 				this.effectState.embodied = pokemon.previouslySwitchedIn;
 				this.boost({atk: 1}, pokemon);
@@ -1193,7 +1193,7 @@ export const Abilities: import('../sim/dex-abilities').AbilityDataTable = {
 	},
 	embodyaspectteal: {
 		onStart(pokemon) {
-			if (pokemon.baseSpecies.name === 'Ogerpon-Teal-Tera' &&
+			if (pokemon.baseSpecies.name === 'Ogerpon-Teal-Tera' && pokemon.terastallized &&
 				this.effectState.embodied !== pokemon.previouslySwitchedIn) {
 				this.effectState.embodied = pokemon.previouslySwitchedIn;
 				this.boost({spe: 1}, pokemon);
@@ -1206,7 +1206,7 @@ export const Abilities: import('../sim/dex-abilities').AbilityDataTable = {
 	},
 	embodyaspectwellspring: {
 		onStart(pokemon) {
-			if (pokemon.baseSpecies.name === 'Ogerpon-Wellspring-Tera' &&
+			if (pokemon.baseSpecies.name === 'Ogerpon-Wellspring-Tera' && pokemon.terastallized &&
 				this.effectState.embodied !== pokemon.previouslySwitchedIn) {
 				this.effectState.embodied = pokemon.previouslySwitchedIn;
 				this.boost({spd: 1}, pokemon);
diff --git a/data/cg-teams.ts b/data/cg-teams.ts
index 826833072007..9ac9d0e85fd4 100644
--- a/data/cg-teams.ts
+++ b/data/cg-teams.ts
@@ -346,8 +346,8 @@ export default class TeamGenerator {
 		const hasTeraBlast = moves.some(m => m.id === 'terablast');
 		const hasRevelationDance = moves.some(m => m.id === 'revelationdance');
 		let teraType;
-		if (species.forceTeraType) {
-			teraType = species.forceTeraType;
+		if (species.requiredTeraType) {
+			teraType = species.requiredTeraType;
 		} else if (item === 'blacksludge' && this.prng.randomChance(2, 3)) {
 			teraType = 'Poison';
 		} else if (hasTeraBlast && ability === 'Contrary' && this.prng.randomChance(2, 3)) {
@@ -728,7 +728,7 @@ export default class TeamGenerator {
 
 		// Oricorio should rarely get Tera Blast, as Revelation Dance is strictly better
 		// Tera Blast is also bad on species with forced Tera types, a.k.a. Ogerpon and Terapagos
-		if (move.id === 'terablast' && (species.baseSpecies === 'Oricorio' || species.forceTeraType)) weight *= 0.5;
+		if (move.id === 'terablast' && (species.baseSpecies === 'Oricorio' || species.requiredTeraType)) weight *= 0.5;
 
 		return weight;
 	}
diff --git a/data/mods/mixandmega/scripts.ts b/data/mods/mixandmega/scripts.ts
index c9c05eaf7d8d..68cb95967561 100644
--- a/data/mods/mixandmega/scripts.ts
+++ b/data/mods/mixandmega/scripts.ts
@@ -434,7 +434,7 @@ export const Scripts: ModdedBattleScriptsData = {
 
 			let type = pokemon.teraType;
 			if (pokemon.species.baseSpecies !== 'Ogerpon' && pokemon.getItem().name.endsWith('Mask')) {
-				type = this.dex.species.get(pokemon.getItem().forcedForme).forceTeraType!;
+				type = this.dex.species.get(pokemon.getItem().forcedForme).requiredTeraType!;
 			}
 			this.battle.add('-terastallize', pokemon, type);
 			pokemon.terastallized = type;
diff --git a/data/pokedex.ts b/data/pokedex.ts
index f80acd870965..286f099d5f42 100644
--- a/data/pokedex.ts
+++ b/data/pokedex.ts
@@ -18195,7 +18195,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		eggGroups: ["Undiscovered"],
 		otherFormes: ["Ogerpon-Wellspring", "Ogerpon-Hearthflame", "Ogerpon-Cornerstone", "Ogerpon-Teal-Tera", "Ogerpon-Wellspring-Tera", "Ogerpon-Hearthflame-Tera", "Ogerpon-Cornerstone-Tera"],
 		formeOrder: ["Ogerpon", "Ogerpon-Wellspring", "Ogerpon-Hearthflame", "Ogerpon-Cornerstone", "Ogerpon-Teal-Tera", "Ogerpon-Wellspring-Tera", "Ogerpon-Hearthflame-Tera", "Ogerpon-Cornerstone-Tera"],
-		forceTeraType: "Grass",
+		requiredTeraType: "Grass",
 	},
 	ogerponwellspring: {
 		num: 1017,
@@ -18212,7 +18212,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		eggGroups: ["Undiscovered"],
 		requiredItem: "Wellspring Mask",
 		changesFrom: "Ogerpon",
-		forceTeraType: "Water",
+		requiredTeraType: "Water",
 	},
 	ogerponhearthflame: {
 		num: 1017,
@@ -18229,7 +18229,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		eggGroups: ["Undiscovered"],
 		requiredItem: "Hearthflame Mask",
 		changesFrom: "Ogerpon",
-		forceTeraType: "Fire",
+		requiredTeraType: "Fire",
 	},
 	ogerponcornerstone: {
 		num: 1017,
@@ -18246,7 +18246,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		eggGroups: ["Undiscovered"],
 		requiredItem: "Cornerstone Mask",
 		changesFrom: "Ogerpon",
-		forceTeraType: "Rock",
+		requiredTeraType: "Rock",
 	},
 	ogerpontealtera: {
 		num: 1017,
@@ -18262,7 +18262,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		color: "Green",
 		eggGroups: ["Undiscovered"],
 		battleOnly: "Ogerpon",
-		forceTeraType: "Grass",
+		requiredTeraType: "Grass",
 	},
 	ogerponwellspringtera: {
 		num: 1017,
@@ -18279,7 +18279,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		eggGroups: ["Undiscovered"],
 		requiredItem: "Wellspring Mask",
 		battleOnly: "Ogerpon-Wellspring",
-		forceTeraType: "Water",
+		requiredTeraType: "Water",
 	},
 	ogerponhearthflametera: {
 		num: 1017,
@@ -18296,7 +18296,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		eggGroups: ["Undiscovered"],
 		requiredItem: "Hearthflame Mask",
 		battleOnly: "Ogerpon-Hearthflame",
-		forceTeraType: "Fire",
+		requiredTeraType: "Fire",
 	},
 	ogerponcornerstonetera: {
 		num: 1017,
@@ -18313,7 +18313,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		eggGroups: ["Undiscovered"],
 		requiredItem: "Cornerstone Mask",
 		battleOnly: "Ogerpon-Cornerstone",
-		forceTeraType: "Rock",
+		requiredTeraType: "Rock",
 	},
 	archaludon: {
 		num: 1018,
@@ -18404,7 +18404,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		eggGroups: ["Undiscovered"],
 		otherFormes: ["Terapagos-Terastal", "Terapagos-Stellar"],
 		formeOrder: ["Terapagos", "Terapagos-Terastal", "Terapagos-Stellar"],
-		forceTeraType: "Stellar",
+		requiredTeraType: "Stellar",
 	},
 	terapagosterastal: {
 		num: 1024,
@@ -18419,7 +18419,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		color: "Blue",
 		eggGroups: ["Undiscovered"],
 		battleOnly: "Terapagos",
-		forceTeraType: "Stellar",
+		requiredTeraType: "Stellar",
 	},
 	terapagosstellar: {
 		num: 1024,
@@ -18434,7 +18434,7 @@ export const Pokedex: import('../sim/dex-species').SpeciesDataTable = {
 		color: "Blue",
 		eggGroups: ["Undiscovered"],
 		battleOnly: "Terapagos",
-		forceTeraType: "Stellar",
+		requiredTeraType: "Stellar",
 	},
 	pecharunt: {
 		num: 1025,
diff --git a/sim/battle-actions.ts b/sim/battle-actions.ts
index 64408001b5fa..600384c68e03 100644
--- a/sim/battle-actions.ts
+++ b/sim/battle-actions.ts
@@ -1932,6 +1932,11 @@ export class BattleActions {
 	}
 
 	terastallize(pokemon: Pokemon) {
+		if (pokemon.species.baseSpecies === 'Ogerpon' && !['Fire', 'Grass', 'Rock', 'Water'].includes(pokemon.teraType)) {
+			this.battle.hint("If Ogerpon Terastallizes into a type other than Fire, Grass, Rock, or Water, the game softlocks.");
+			return;
+		}
+
 		if (pokemon.illusion && ['Ogerpon', 'Terapagos'].includes(pokemon.illusion.species.baseSpecies)) {
 			this.battle.singleEvent('End', this.dex.abilities.get('Illusion'), pokemon.abilityState, pokemon);
 		}
@@ -1946,10 +1951,11 @@ export class BattleActions {
 		pokemon.knownType = true;
 		pokemon.apparentType = type;
 		if (pokemon.species.baseSpecies === 'Ogerpon') {
-			const tera = pokemon.species.id === 'ogerpon' ? 'tealtera' : 'tera';
-			pokemon.formeChange(pokemon.species.id + tera, null, true);
+			let ogerponSpecies = toID(pokemon.species.battleOnly || pokemon.species.id);
+			ogerponSpecies += ogerponSpecies === 'ogerpon' ? 'tealtera' : 'tera';
+			pokemon.formeChange(ogerponSpecies, null, true);
 		}
-		if (pokemon.species.name === 'Terapagos-Terastal' && type === 'Stellar') {
+		if (pokemon.species.name === 'Terapagos-Terastal') {
 			pokemon.formeChange('Terapagos-Stellar', null, true);
 			pokemon.baseMaxhp = Math.floor(Math.floor(
 				2 * pokemon.species.baseStats['hp'] + pokemon.set.ivs['hp'] + Math.floor(pokemon.set.evs['hp'] / 4) + 100
diff --git a/sim/dex-species.ts b/sim/dex-species.ts
index dacfdc48f96b..2e6f99bbb496 100644
--- a/sim/dex-species.ts
+++ b/sim/dex-species.ts
@@ -226,7 +226,7 @@ export class Species extends BasicEffect implements Readonly<BasicEffect & Speci
 	/** True if a Pokemon species is incapable of dynamaxing */
 	readonly cannotDynamax?: boolean;
 	/** The Tera Type this Pokemon is forced to use */
-	readonly forceTeraType?: string;
+	readonly requiredTeraType?: string;
 	/** What it transforms from, if a pokemon is a forme that is only accessible in battle. */
 	readonly battleOnly?: string | string[];
 	/** Required item. Do not use this directly; see requiredItems. */
diff --git a/sim/pokemon.ts b/sim/pokemon.ts
index 91bd3a9095ce..bd0e7cf6481f 100644
--- a/sim/pokemon.ts
+++ b/sim/pokemon.ts
@@ -514,6 +514,14 @@ export class Pokemon {
 	getUpdatedDetails(illusionLevel?: number) {
 		let name = this.species.name;
 		if (name === 'Greninja-Bond') name = 'Greninja';
+		if (this.species.baseSpecies === 'Ogerpon' && this.terastallized && this.teraType !== this.species.requiredTeraType) {
+			switch (this.teraType) {
+			case 'Grass': name = 'Ogerpon-Teal-Tera'; break;
+			case 'Water': name = 'Ogerpon-Wellspring-Tera'; break;
+			case 'Fire': name = 'Ogerpon-Hearthflame-Tera'; break;
+			case 'Rock': name = 'Ogerpon-Cornerstone-Tera'; break;
+			}
+		}
 		const level = illusionLevel || this.level;
 		return name + (level === 100 ? '' : ', L' + level) +
 			(this.gender === '' ? '' : ', ' + this.gender) + (this.set.shiny ? ', shiny' : '');
@@ -1399,6 +1407,9 @@ export class Pokemon {
 			if (!source) {
 				// Tera forme
 				// Ogerpon/Terapagos text goes here
+				if (species.baseSpecies === 'Ogerpon' && this.terastallized && this.teraType !== species.requiredTeraType) {
+					this.battle.hint(`Ogerpon terastallized into ${species.name}, but it has taken the appearance of ${this.details.split(",")[0]} due to its tera type being ${this.teraType}.`);
+				}
 			} else if (source.effectType === 'Item') {
 				this.canTerastallize = null; // National Dex behavior
 				if (source.zMove) {
diff --git a/sim/team-validator.ts b/sim/team-validator.ts
index a498f17267e4..a11e12ed14c1 100644
--- a/sim/team-validator.ts
+++ b/sim/team-validator.ts
@@ -582,10 +582,6 @@ export class TeamValidator {
 			name = `${set.name} (${set.species})`;
 		}
 
-		if (!set.teraType && this.gen === 9) {
-			set.teraType = species.types[0];
-		}
-
 		if (!set.level) set.level = ruleTable.defaultLevel;
 
 		let adjustLevel = ruleTable.adjustLevel;
@@ -682,13 +678,12 @@ export class TeamValidator {
 				set.hpType = type.name;
 			}
 		}
-		if (species.forceTeraType) {
-			set.teraType = species.forceTeraType;
-		}
-		if (set.teraType) {
-			const type = dex.types.get(set.teraType);
+		if (set.teraType || this.gen === 9) {
+			const type = dex.types.get(set.teraType || species.requiredTeraType || species.types[0]);
 			if (!type.exists || type.isNonstandard) {
 				problems.push(`${name}'s Terastal type (${set.teraType}) is invalid.`);
+			} else if (species.requiredTeraType && species.requiredTeraType !== type.name && ruleTable.has('obtainablemisc')) {
+				problems.push(`${species.name}'s Terastal type needs to be ${species.requiredTeraType}, please fix it.`);
 			} else {
 				set.teraType = type.name;
 			}
diff --git a/test/sim/misc/ogerpon.js b/test/sim/misc/ogerpon.js
index 21b7deeaeb79..e0bd5d2fab43 100644
--- a/test/sim/misc/ogerpon.js
+++ b/test/sim/misc/ogerpon.js
@@ -20,4 +20,108 @@ describe(`[Hackmons] Ogerpon`, function () {
 		battle.makeChoices('switch 2', 'auto');
 		assert.equal(ogerpon.ability, 'embodyaspectteal', `Ogerpon's ability should be Embody Aspect after switching out`);
 	});
+
+	it(`won't Terastallize into a type other than Fire, Grass, Rock or Water`, function () {
+		battle = common.gen(9).createBattle([[
+			{species: 'ogerponwellspringtera', ability: 'embodyaspectwellspring', moves: ['sleeptalk'], teraType: 'Electric'},
+		], [
+			{species: 'silicobra', moves: ['stealthrock']},
+		]]);
+		const ogerpon = battle.p1.active[0];
+		battle.makeChoices('move sleeptalk terastallize', 'auto');
+		assert.false(!!ogerpon.terastallized);
+	});
+
+	// https://www.smogon.com/forums/threads/ogerpon-teal-tera-tera-can-exist.3742851/post-10132811
+	it(`can Terastallize into the type of another mask`, function () {
+		battle = common.gen(9).createBattle([[
+			{species: 'ogerponwellspring', ability: 'waterabsorb', moves: ['ivycudgel'], teraType: 'Rock'},
+		], [
+			{species: 'seismitoad', ability: 'waterabsorb', moves: ['stealthrock']},
+		]]);
+		const ogerpon = battle.p1.active[0];
+		battle.makeChoices('move ivycudgel terastallize', 'auto');
+		assert.species(ogerpon, 'Ogerpon-Wellspring-Tera');
+		assert.equal(ogerpon.ability, 'embodyaspectwellspring');
+		assert.statStage(ogerpon, 'spd', 1);
+		assert.equal(ogerpon.getTypes().join(''), 'Rock');
+		assert.fullHP(battle.p2.active[0]);
+		assert(battle.log.includes('|detailschange|p1a: Ogerpon|Ogerpon-Cornerstone-Tera, F, tera:Rock'));
+	});
+
+	// https://www.smogon.com/forums/threads/ogerpon-teal-tera-tera-can-exist.3742851/post-10132811
+	it(`Tera form can Terastallize`, function () {
+		battle = common.gen(9).createBattle([[
+			{species: 'ogerponwellspringtera', ability: 'embodyaspectwellspring', moves: ['ivycudgel'], teraType: 'Water'},
+		], [
+			{species: 'seismitoad', ability: 'waterabsorb', moves: ['stealthrock']},
+		]]);
+		const ogerpon = battle.p1.active[0];
+		battle.makeChoices('move ivycudgel terastallize', 'auto');
+		assert.species(ogerpon, 'Ogerpon-Wellspring-Tera');
+		assert.equal(ogerpon.ability, 'embodyaspectwellspring');
+		assert.statStage(ogerpon, 'spd', 1);
+		assert.equal(ogerpon.getTypes().join(''), 'Water');
+		assert.fullHP(battle.p2.active[0]);
+		assert(battle.log.includes('|detailschange|p1a: Ogerpon|Ogerpon-Wellspring-Tera, F, tera:Water'));
+	});
+
+	// https://www.smogon.com/forums/threads/ogerpon-teal-tera-tera-can-exist.3742851/post-10132811
+	it(`Tera form can Terastallize into the type of another mask`, function () {
+		battle = common.gen(9).createBattle([[
+			{species: 'ogerponwellspringtera', ability: 'embodyaspectwellspring', moves: ['ivycudgel'], teraType: 'Rock'},
+		], [
+			{species: 'seismitoad', ability: 'waterabsorb', moves: ['stealthrock']},
+		]]);
+		const ogerpon = battle.p1.active[0];
+		battle.makeChoices('move ivycudgel terastallize', 'auto');
+		assert.species(ogerpon, 'Ogerpon-Wellspring-Tera');
+		assert.equal(ogerpon.ability, 'embodyaspectwellspring');
+		assert.statStage(ogerpon, 'spd', 1);
+		assert.equal(ogerpon.getTypes().join(''), 'Rock');
+		assert.fullHP(battle.p2.active[0]);
+		assert(battle.log.includes('|detailschange|p1a: Ogerpon|Ogerpon-Cornerstone-Tera, F, tera:Rock'));
+	});
+
+	// https://www.smogon.com/forums/threads/scarlet-violet-battle-mechanics-research.3709545/post-10404934
+	it(`can Terastallize into any type if transformed, but it won't change form`, function () {
+		battle = common.gen(9).createBattle([[
+			{species: 'ogerponwellspring', ability: 'waterabsorb', moves: ['transform', 'ivycudgel'], teraType: 'Fairy'},
+			{species: 'silicobra', moves: ['stealthrock']},
+		], [
+			{species: 'seismitoad', ability: 'waterabsorb', moves: ['sleeptalk']},
+		]]);
+		const ogerpon = battle.p1.active[0];
+		battle.makeChoices('move transform', 'auto');
+		battle.makeChoices('move sleeptalk terastallize', 'auto');
+		assert.equal(ogerpon.baseSpecies.name, 'Ogerpon-Wellspring');
+		assert.species(ogerpon, 'Seismitoad');
+		assert.equal(ogerpon.getTypes().join(''), 'Fairy');
+
+		battle.makeChoices('switch 2', 'auto');
+		battle.makeChoices('switch 2', 'auto');
+		battle.makeChoices('move ivycudgel', 'auto');
+		assert.species(ogerpon, 'Ogerpon-Wellspring');
+		assert.equal(ogerpon.ability, 'waterabsorb');
+		assert.statStage(ogerpon, 'spd', 0);
+		assert.equal(ogerpon.getTypes().join(''), 'Fairy');
+		assert.fullHP(battle.p2.active[0]);
+		assert.false(battle.log.includes('|detailschange|'));
+	});
+
+	// https://www.smogon.com/forums/threads/ogerpon-teal-tera-tera-can-exist.3742851/post-10132811
+	it(`Embody Aspect should not activate unless the user is Terastallized`, function () {
+		battle = common.gen(9).createBattle([[
+			{species: 'ogerponwellspringtera', ability: 'embodyaspectwellspring', moves: ['sleeptalk'], teraType: 'Water'},
+		], [
+			{species: 'silicobra', moves: ['stealthrock']},
+		]]);
+		const ogerpon = battle.p1.active[0];
+		battle.makeChoices();
+		assert.species(ogerpon, 'Ogerpon-Wellspring-Tera');
+		assert.statStage(ogerpon, 'spd', 0);
+		battle.makeChoices('move sleeptalk terastallize', 'auto');
+		assert.species(ogerpon, 'Ogerpon-Wellspring-Tera');
+		assert.statStage(ogerpon, 'spd', 1);
+	});
 });