Idea off the top of my head that I would love to see done if it is even possible to code.
Skill: Blood Gamble
Cost: 100 HP + 200 Mana
CD: 20 seconds
Basic effects: The Bloodmage spends 100 health to deal 100 damage in an AOE around him, plus healing allies in the area for 100 health.
Bonus Effect 1: If more allies are healed then enemies damaged, the Bloodmage receives 50 damage for every extra member healed and those he healed lose 25 health.
Bonus Effect 2: If the Bloodmage damages more targets then are healed, the Bloodmage receives his 100 health from the cast back plus deals 25 extra damage for every extra enemy. This effect will instead cause the bloodmage to lose half his current health plus become become silenced and invulnerable if no players are healed.
Bonus Effect 3: If both sides are even the Bloodmage will receive half his health back from the cast.
Examples in case you can't decipher what I said because you feel I have terrible wording
Example 1: 5 players including the Bloodmage against 5 players, if the skill hits all of them the Bloodmage is healed 50 health
Example 2: 6 players including the Bloodmage against 4 players, if the skill hits all of them the Bloodmage is dealt a 100 damage penalty (That is 50 health from each additional ally) and 25 health is taken from all those he healed.
Example 3: 4 players including the Bloodmage against 6 players, if the skill hits all of them the Bloodmage is refunded the cost of the skill plus he deals an additional 50 damage. (25 damage from each additional enemy player)
Example 4: So you felt like soloing a full party of 10 because this skill would do so much damage while your alone, you're half right. The skill will deal the 100 damage AOE but then cut your current health in half, make you invulnerable and unable to attack or use skills to heal yourself like those silly Clerics.