Doc
HP: 100
Lore: Wandering healer

Passive: Blood Collector - Whenever an enemy is dealt damage, Doc gains a blood charge. This applies per source.

Surgical Slice
Cost: Black
Cooldown: 0
Classes: Instant, Melee
Deals 15 piercing physical damage to one enemy.

Ventus Shield
Cost: Blue
Cooldown: 1
Classes: Buff
Prevents the next 25 physical damage one ally will take, and heals them for 5 life per turn while the shield persists.

Cosmic Shield
Cost: Blue Black
Cooldown: 2
Classes: Buff
Prevents the next 30 magical damage one ally will take, and heals them for 10 life per turn while the shield persists.

Pox
Cost: Blue Blue
Cooldown: 4
Classes: Instant, Ranged
Consumes all blood charges, dealing 10 magic damage per blood charge consumed to one target.

Doc's passive only affects his fourth ability, Pox.

Surgical Slice represents a reliable source of damage, and is thus valuable to a lot of comps. Its primarily appreciated in the mercenary teamcomp because it can be comboed with marking knife to deal 35 damage for a relatively small amount of energy pretty consistently. It also serves as an easy way for Doc to stack Pox.

Ventus shield is one of Doc's two defining abilities. Its a very efficient damage prevention skill, and is generally a good way to keep people alive. Ventus shield stacks, so if you have 5 points left on one shield, and apply a new one, the opponent will have to deal a full 25 damage to prevent further healing.

Cosmic shield is Ventus shield's more interesting mirror. Magic damage is rarer than physical damage, so against a comp with no reliable source of magic damage, cosmic shield becomes an efficient healing skill. The Ventus/Cosmic shield combo also demonstrates how magic damage is more expensive to prevent.

Pox is what makes Doc an interesting character, as he's very vanilla otherwise. Pox is a huge threat that grows as time goes on. Because of this, opponents will want to kill doc within a few turns, otherwise they risk getting hit by a high-stacked Pox.

In the mercenary teamcomp, the dual threats of Doc and Axiom divide your opponents attention. The comp has plenty of ways to protect these two threats while building up to kill off one or more major components of the enemies team. All three members of the team are reasonably well equipped to duel in a 1v1, so as long as they get a good start, they're well equipped to follow it up and win.