Mechanics Me First interactions with Choice items

[isatrapp]

What type of bug are you reporting? Mechanics

What is the bug?
It's a Me First bug. Bulbapedia states: " In Generation V only, if a Pokémon holds a Choice item and uses Me First, it will not become locked into any move, and is free to select a different move on a later turn. In all other generations, it will become locked into Me First, rather than the move it copied (if any, and even if the Pokémon knows that move separately in one of its own move slots). " However, this is not true when done in battle.

Secondly, Me First is restricted by Assault Vest. Bulbapedia states:" The Assault Vest does not prevent a Pokémon from selecting Me First, the only status move for which this is the case. " However, a Pokemon with only Me First holding an Assault Vest will be forced to use struggle.

Are you able to replicate it? If so, how?
Gen 5, target is locked into Me First
Just load up a choiced mon w/ Me First in bw.
Gen 6, Me First is restricted by Assault Vest
Load up any mon w/ Me First with assault vest in oras

 

[DaWoblefet]

This is actually even more complicated than Bulbapedia details. It is mistaken about Choice items and Me First in Gen V; the same behavior occurs in Gens 5-7.

Gen 7
Selectable through Assault Vest and Taunt
Choice locked on success
Not Choice locked on failure due to moving second or using into status move; does use PP in both cases

Gen 6 - Identical to Gen 7

Gen 5
Selectable through Taunt
Choice locked on success
Not Choice locked on failure due to moving second or using into status move; does use PP in both cases

Gen 4
Not selectable through Taunt
Choice locked on success, failure due to moving second, or using into status move

In addition, while researching this, I found that Mirror Move has the same properties as Me First and Sleep Talk if they can't find a move to call - that is, they won't get Choice locked, but will use PP. Assist and Copycat don't have this behavior (Metronome and Nature Power will always successfully call a move, so they can't fail to find a move to call). In general, Showdown could stand to refactor a lot of its checks for status moves to actually be a check for base power not being 0.

I fixed the behavior with Assault Vest, but the Choice locking behavior will be more challenging to implement. We'll need a new event to handle setting the moves a lot earlier than what we're currently doing.