There are a few TTRPGs that let you build a magic system for yourself. The most developed one is called Ars Magica. I recently discovered a newer game called Tattered Magicks that also lets you craft magic for your spellcaster.
D&D is fun, but it’s not the only rpg out there
Sonic 2! Let the 5yo be tails! He’ll never die. He can collect rings and kill enemies. It’s the best 2 player platformer ever created