The substitute is created at the cost of 25% of the users HP and will take all or most of the incoming damage from the opposing Pokémon until it breaks. A substitute cannot be created if your Pokémon's health is less than 25% of its maximum HP. A one-hit KO attack will always break a substitute if it hits.
With the release of Generation VI, sound based moves such as Hyper Voice and Growl can bypass a Substitute and affect the user directly. As well, Generation VI made it so that a Pokemon with the ability Infiltrator can hit a target using Substitute.
Moves that can bypass a substitute and damage the user:
- Bug Buzz
- Disarming Voice
- Echoed Voice
- Relic Song
Further, moves that do not damage the user but bypass their substitute and affect them in other ways:
- Grass Whistle
- Metal Sound
- Noble Roar
- Parting Shot
- Perish Song
Plus, any move used by a Pokemon with the ability infiltrator will bypass the substitute and affect the target directly, opening the door for a wider range of attacks not listed here.
In Generations I and II, the Substitute takes the appearance of a Rhydon. In all subsequent games it is a plush toy that is said to resemble a Larvitar. However, some contend that it resembles the being inside Kangaskhan's pouch. When the move is used, the user appears to jump back to the sidelines leaving a puff of smoke in its wake. From this the Substitute appears. When a user attacks while it is active, the substitute will move out of the way while the user comes back onto the battlefield. Once the users move is complete they return to their location off-screen and the substitute takes it's place once more.