Tundra Giants are both ranged and melee attackers who posses typical giant strength. They tend to use their ranged attack (a giant thrown rock) to pummel enemies approaching them, then they use their massive fists to bash their foes in melee with powerful hammerskills. For some reason, they carry a pack of tree trunks on their backs.
Like most giants and some other creatures (such as Abyssals), Tundra Giants will knock characters down on every critical hit. Because they almost always come in tightly packed groups, Dulled Weapon or Stone Sheath can make them significantly less frustrating.
Occasionally when they get down to about 10% health, they will somehow be healed for a small amount. Whether this is a bug or intentional is yet to be discovered.