Armello

River is a combat heavy hero with a fantastic hero skill whereby she can fire an arrow and do 1 damage to an enemy before engaging them in battle.

Fight: 4
Body: 5
Wits: 4
Spirit: 3
Gold: 3

This skill makes her the prime candidate for killing the king, as you can wait until the king is down to 1 health via rot damage, then attack him and he will die from your hero skill without having to endure the random dice rolls of battle. Or, alternatively, she is strong enough that a prestige victory should also be easy.