StarCraft II: Heart of the Swarm/New Terran units

Hellbat
Hellions can transform into tougher, slower and stronger walkers with shorter range but the splash damage is wider, and Hellbats require researching at the armory. Do not send these units after Marauders, Siege Tanks, Thors, Roaches, Ultralisks, Stalkers or immortals.

Widow mine
Widow mines burrow and launch missiles at enemy units and causes major damage in a radius. Has a slow rate of fire however and weak against detectors.

Warhound
Basically a modified Goliath but does great damage to mechanical units only.

Reaper
It cannot be upgraded with its speed boost upgrade but can self heal itself outside of battle.

Hellion
Can now transform into the Hellbat if it is researched at the armory.

Siege tank
Does not need upgrade to switch to siege mode and tank mode.

Thor
Can now switch between two modes, Explosive payload and the Punisher cannons. In explosive payload mode it does splash damage to multiple air units but with Punisher cannons it will do serious damage to single air units but it has a slow rate of fire.

Medivacs
Can now use a speed boost to get to places faster.

Battlecruisers
Yamato cannons take up 100 energy instead of 125.