tip characters ala Nostale

You can use Nostale character system.
First, you have 3 types.
On map, you can do special hard dungeons. When complete, win card with new character. card have energy and can updgrade by special items. Use energy, when have card, when lose energy, lose character mode. When not in special character, energy go up. I have in nostale about 5 characters cards. Best is ninja for self healing skill.