^ Fail, you need a monk in the middle, monk in back left and right, and witch in between all 3!
Anyway, on topic...
I'd make a Jesus merc. He'd be staff (of course) and have;
Targeted skill, infinite duration when cast will save the targeted merc from a killing blow. Raising the skill level will increase the amount of HP regained by the merc that Jesus saves.
Takes Half Damage
Passive skill, Jesus takes half damage. Raising the skill level grants a higher chance to take LESS than half damage, up to a maximum of -75% damage taken.