It could work just like a flesh golem does for the necromancer except better autonomous AI listed below.
Robot uses rockets when 2 or more enemies are in a 1000 radius
Minigun when only 1 foe is present in 1000 radius
Flamethrower if enemy is up close
Activating the skill makes the robot whirl in place knocking back foes.
At 10% health the robot begins a self destruct sequence;
after 8 seconds the robot will explode if not killed in time and damages and burns enemies in a 600 radius. players can AoE heal the robot to greater than 10% to stop the self destruct countdown.
Behavior in targeting can be the same as turrets.
This elite skill may not see the light of day in WvW , but I see its usefulness in PvE and Spvp.