Deerhunter along with Lumberjack were hired by an unknown employer to take out the Raven. He apparently doesn't think highly of Lumberjack as he calls him a pathetic excuse for a Raven. He is encountered in the mission Eliminate the Raven.
Tsaden is a lightweight two-legged AC equipped with anti missile extensions, a grenade rifle, a laser blade, a dual back general magazine that increases the units ammo capacity and an overboost core. The unit is also capable of ignoring weight restrictions.
Far more dangerous than Lumberjack; Deerhunter has a grenade rifle that can deal serious damage to your AC. On top of that, he has extra ammo due to his dual back general magazine and he is also adapted (anti-missile extensions), rendering any form of missiles against him, useless. Try to avoid his grenade rifle, and the fight might hurt less, but he might still back it up with his laser blade, so you will have to be on the move. You'll need to preserve AP (and ammo) to fight him.