Eject Button

Switches out when hit. (Hold)

Eject Button forces your Pokémon to switch out when it takes damage from an attack. It's consumed after use, but it gives you a free switch into whatever Pokémon you want without losing momentum.

This item is a bit niche but can be really useful for gaining positional advantage. It's good on Pokémon that want to get in, do something useful like set up weather or spikes or land a hit, and then immediately get out.