This is an add-on for Summon System for RPG Maker MV & MZ by Aerosys (itch.io)

By default, every summoner can summon any pet that the party owns at this point in time. This addon makes the player build a deck first that ultimately defines the pets the summoner can choose from in battle.

The menu comes with many customization parameters for you!

You, as the game dev, can decide when the player can update their deck, e.g., any time or only in specific locations like their home base. You can also define the deck size and increase (or decrease) it permanently or temporarily through traits, equipment, side mission rewards, etc.

Instructions

Deck Addon for Summon System – Aerosys' Blog