Death Must Die - Merris - Difficulty 20 - Summoner Gameplay 

-Example of Merris gameplay using the Summoner sign. The Necromancer's Amulet is being used here to make for easy farming but you can also use certain God cards to get the same effect.
-Also items can be found that have permanent summons on weapons and gear which can benefit from this.
I recommend getting TIme Lord special attack enhancement, and Gem High and a few area of effect abilities. It is pretty flexible once you get going. For yourself you can get as much health and armor upgrades as you can find or damage prevention just to prevent sudden death. If you see other summon cards take those as well if you don't have the Necromancer's Amulet.