Ashbone Pyro one of two self-destructive demons that belong to Shadow. Along with Unstable Demon, these creatures' life constantly drains away. To counteract this, they have ability to sap life from their target in combat, thus to stay alive, they must be in combat or be healed.
Without upgrades, this creature is unable to sustain its life unless it is attacking a buildings, where it gains enough of a damage bonus for life stealing to counter its life drain. However, once upgraded, its damage and life stealing become more effective allowing it to outlast many other creatures due to this. For example, the fully-upgraded Ashbone Pyro heals itself at a net rate of 48.75 (upgraded_damage * siege_bonus * upgraded_lifestealer - instability = 85 * 1.5 * 0.5 - 15) life per second when attacking Buildings. By comparison, a fully upgraded Shaman II is capable of healing 28 life per second.
Perhaps the biggest weakness of this creature is the Nightfire Jet attack ability's short range. Ashbone Pyro must be closer to its target, unlike Long Range units like Firedancer or Fire Stalker which can do their damage outside of the reach of most towers. The Nightfire Jet does have advantages to offset its short range. As a ranged attack, it makes Ashbones a little more responsive to micromanagement or the appearance of new enemies than a melee attack would be. In addition to that, it deals its damage every second, meaning that it spends as little time as possible killing each target and can move on to new targets rapidly. It also allows them to kill air units and enjoy limited ability to shoot at towers perched on cliff edges.
A group of Ashbone Pyros backed up by Viridya or a regeneration spell such as Ray of Light or Regrowth make a fantastic tank for almost any situation, particularly enemy melee units without L damage.
Damage Boost Cards, first and foremost, as it gets an advantage beyond the usual with the Pyro's Life Stealing. As with all Life Stealer Cards, using Damage Boost Cards on Ashbones gives the advantage of increasing the self-healing attribute of their attack