I can fill you in for what the battle would be like.
I presume by "Yu-gi-oh style" he would want:
A feature that allows players to edit a deck of at least 40 cards and a max of 60 cards, with no more than 3 copies of the same card.
This feature would also include an "Extra Deck" where Synchro, Fusion and Xyz monsters would be to a max of 15.
As well as a "Side Deck" where up to 15 cards can be stored and traded between the main deck between battles.
There are 3 types of cards, being: Monsters, Spells and Traps.
Monsters can be expanded into: Normal Monsters, Effect Monsters, Spirit Monsters, Toon Monsters, Gemini Monsters, Tuner Monsters, Synchro Monsters, Xyz Monsters, Fusion Monsters, Ritual Monsters and Union Monsters.
Every monster has a type which can be: Aqua, Beast, Beast-Warrior, Dinosaur, Divine-Beast, Dragon, Fairy, Fiend, Fish, Insect, Machine, Plant, Psychic, Pyro, Reptile, Rock, Sea-Serpent, Spellcaster, Thunder, Warrior, Winged-Beast or Zombie.
Every monster has an attribute which can be: Dark, Divine, Fire, Earth, Light, Water or Wind
Every monster has a level between 1 and 12, except for Xyz monsters that have ranks instead of levels.
Every monster has an ATK and a DEF stat.
Spells can be expanded to: Normal Spells, Equip Spells, Quick-Play Spells, Ritual Spells, Field Spells and Continuous Spells.
And I give up at this point, I haven't even gotten to a fraction of the rules or mechanics.
Even at this point it would be super hard to code everything, a Yu-Gi-Oh system in RPG Maker would take years to complete.