Checks if a Pokemon is allowed under a challenge, and allowed in battle.
If both are true, returns null.
If one of them is not true, returns message content that the Pokemon is invalid.
Typically used for cheecking whether a Pokemon can be selected for a MysteryEncounterOption
Checks if a Pokemon is allowed under a challenge, and allowed in battle. If both are true, returns
null. If one of them is not true, returns message content that the Pokemon is invalid. Typically used for cheecking whether a Pokemon can be selected for a MysteryEncounterOption