Earth Elemental. Base 10 health. 12 with Llama. 18 with last stand. Regenerates 6 health per turn and has attack or 3 or 5 (depending on level) once last stand kicks in. It only costs 6 so llama/elemental only 13 power. At 13 power nothing can deal out more than 6 damage per turn so elemental wipes out any opposition. In the odd case of armored defender with repair support the elemental won't be able to damage the opponent but once fatigue kicks in the elemental still wins in the end.