A low cost frontline Mini to help soak up some damage. Skeleton Guard only has 5 HP, so it's not really a tank, but can be upgraded to have a shield at the start of the round to get +7/12 temporary HP to help it survive.
"Super: Gain 7 Shield for a short time"
Shield effect gives him a temporary new HP bar that lasts about 5 seconds. During this super, Skeleton Guard can still attack but can't get any energy.