How does Terastal work?

I have no idea how to spell or pronounce the new gimmick so I’m not even gonna try. I heard that the gimmick supposedly adds an extra type and stab to your Pokemon and a new move named tera blast which I’d assume becomes the same type as the gimmick. So, aside from the tera blast, what exactly does the gimmick do? Take a Garchomp for example. If you do something like using a steel type of the gimmick, will Garchomp become a triple type with dragon / ground / steel or will its tera blast simply become a steel type but Garchomp doesn’t gain an extra type? Would it work the same way with a single type Pokemon like Haxorus or Tornadus where they get a second type?

This is of course assuming I got the idea right because I could be entirely wrong about this but there have been a lot of leaks right now. So, back to the original question, what exactly are the details of this new gimmick and how does it work?

Pleaselog inorregisterto add a comment.

Terastalis a special ability that can be activated during a battle, similar to Mega Evolution. When you activate it, your Pokemon will beterastallisedfor the remainder of that battle. You can only terastallise one Pokemon per battle.

The principal effect of terastallising is that it changes your Pokemon’s type to itsTera Type. Your Pokemon’s Tera Type is a trait that it carries, similar to its nature or ability. It is possible tochange your Pokemon’s Tera Type using a currency called Tera Shards. Any Pokemon may have any type as its Tera Type.

For example, if I have a Salamence whose Tera Type is Steel, it will change from a Dragon/Flying-type to a pure Steel-type when it terastallises. Defensively, Salamence will now behave like any other Steel-type; it will be weak to Fire, immune to Poison, etc. If Salamence’s Tera Type were Dragon instead, then it would transform to a pure Dragon-type (thereby losing its Flying type, and therefore its immunity to Ground, etc).

Terastal is a bit different offensively. It has some effects that go against the present intuition of how Pokemon types work. Hopefully, this list is digestible:

A concise way of putting it is: “Terastal adds 0.5 to the STAB multiplier of the Pokemon’s Tera Type, and changes its defensive type to match the Tera Type.”

Tera Blast’s type follows your Pokemon’s Tera Type after terastallising, and is Normal-type otherwise.

Source(includes a longer discussion of Terastal mechanics, including what happens to Adaptability, what order boosts apply, and more)

Well for starters, most people are just referring to the new gimmick as “tera types” so that’s what I’m going to be using. Tera types don’t actually add a type, they replace the original typing(s) of the Pokémon with the new single typing of the tera type. For example, if a Gliscor had a ghost teratype, it’s original ground & flying dual type would be replaced with a singular ghost type.

This also affects STAB, but in a funky way. Rather than losing the STAB of Gliscors original typing, he would have the STAB of ghost in addition to ground and flying. This allows for 3 different STABS on a single Pokemon, which is pretty remarkable for competitive. In the case of a tera type in which is the same as the original typing, the STAB of that doubled up type would gain a 2x damage multiplier rather than the original 1.5x multiplier. So in the case of Gliscor, having a ground type tera type means his flying moves would deal 1.5x damage and his ground moves would deal 2x damage.

This is all the info that I’ve observed so far. Take it with a grain of salt, because most of my sources are leaks and theories, but hopefully this helps explain the complexity behind this new gimmick.