Double Strike - a damage bonus of approximately 150% (not 2, because a counterattack follows the first strike).
Unanswerable Strike - a damage bonus of 200% (strikes twice, receiving retaliation only after the second hit).
Flight and ranged attack.
Ranged attack provides a creature power increase of 20-50%.
Flight should also provide some bonus, as well as mass attack (magogs, cerberi, liches, psi-elementals, hydras), vampiric lordism, mana drain (ghosts, upgraded imps, pegasi, mages), magic immunity (necromancers, dwarves, unicorns, ifrits, the elemental company with phoenixes, dragons, etc.), gorgonism, phoenix rebirth, and much more.