Maybe one that can heal you, like 15% chance to heal 100 hp on attack
Did you use pulverize (% chance to deal AOE damage on attack)?
Increased specific attribute (prolly primary attribute for that hero)
Lifesteal, but for mana, so when you attack you can steal some of targets mana
Degeneration auras that slow enemies atk/move speed, damage, armor
Extra range, move/atk speed, more damage, armor, etc
Armor reduction (orb of corruption)
If you play DotA there are many good passive abilities, like when you kill unit, you regen a % of their health, you have a % chance to attack 2 times in one attack, when you attack enemy from back you deal bonus damage (agility multiplied by lvl of ability or sumthin like that), feedback (depleats enemies mana when you atk em), when a nearby enemy has low hp you gain bonus move speed and get vision of them.