How to make a Pokemon appear in the field when the player has a specific item or Pokemon

[AztecCroc]

How do I make a Pokemon appear in the field when the player has a specific item (ie. if the Player has the Dark Stone then Zekrom will appear in a specific location, etc.), and have them only appear when the player has the item. Also the same sort of thing but requiring the player to have certain Pokemon in their party instead of a specific item.

 

[HarmonyConcept]

Regarding your first question, I guess you could turn a switch on when you give the item to the player and make the Zekrom appear when that switch is on. It should work if your item cannot be deleted by the player.

For your second question, you can refer to the wiki "Manipulating Pokemon", especially to the function "pbHasSpecies?(:CELEBI)".