Mega Evolution, Z-Moves and Terastallization
Coming to PokeRival, not playable yet. What the three battle gimmicks will do, what is already built, and what still has to land.
In short
- None of the three can be used in battle yet. The option does not appear when you choose a move, and a request for one is ignored.
- The rules are written and tested. What is missing is a way to get the items and the balance work that has to come with them.
- When they arrive, each side gets one gimmick per battle: a Mega, a Z-Move or a Tera, not one of each.
- This page will say so the day that changes, and so will the news.
Why they are switched off
All three change who wins a battle more than almost anything else in the game. Turning them on before Mega Stones and Z-Crystals can be earned would hand them only to whoever happened to be holding the right item, and Terastallization on its own would arrive months ahead of the other two. They come back together, with a way to earn them.
Mega Evolution
A Pokemon holding its own Mega Stone, Charizardite X for a Charizard or Venusaurite for a Venusaur, will be able to Mega Evolve once per battle, before anything moves that turn. The Mega form brings new base stats, often a new ability and sometimes a new type, recomputed from your Pokemon's own IVs, EVs, nature and level. HP stays as it was, and the form ends with the battle.
The Pokedex already shows every Mega form's stats, ability and types beside the base form.
Getting a Mega Stone
No Mega Stone can be obtained in Horos yet. The stones are listed in the item database so you can read what each one is for, but no shop sells them and no quest gives one out.
Z-Moves
A Pokemon holding a Z-Crystal, Firium Z, Waterium Z, Normalium Z and the rest, will be able to turn one move of the crystal's type into its Z-Move, once per battle. A damaging move becomes far stronger, scaled from the original's power: Inferno Overdrive for Fire, Hydro Vortex for Water. A status move keeps its effect and gains a bonus, usually a stat boost.
Getting a Z-Crystal
No Z-Crystal can be obtained in Horos yet. Like the Mega Stones, they are in the item database and nowhere else.
Terastallization
Every Pokemon you own already has a Tera type, shown in its details. A starter's is its first type; a caught or hatched Pokemon's is rolled from the eighteen when it joins you, so it is already part of what makes one catch better than another.

When Terastallization arrives, a Pokemon will be able to become its Tera type for the rest of the battle. Defensively it is only that type from then on, so a Water Pokemon that Teras to Steel stops fearing Grass and starts fearing Fire. Offensively it keeps STAB on its old types and gains it on the new one. No item is needed.
What you can do now
Nothing you do today is wasted. A Pokemon you catch now keeps its Tera type, and a Charizard you raise now will Mega Evolve the day the stones arrive. Until then the battles are decided by the type chart, abilities, held items, weather and status, all of which work: How battles work is the place to start.