Early and midgame core
Bone Guard and Skeleton Archer form the clearest reported early pair: a frontline to absorb pressure and a ranged unit to keep damage flowing. If you only own starter units, keep role coverage instead of chasing rarity alone.
For midgame, community guides point toward Mighty Orc as a longer-term frontline. Lava Imp adds reported burn damage, while Skeleton Archer remains a practical fallback when upgrades are already invested.