The Robo Duck was an April fools prank by pixonic.
Pixonic's description of it:
Roboduck is a new ultraheavy robot with the highest durability among other robots of the same class. Roboduck can sit on beacons without allowing the enemies to intercept.
Along with the significant endurance, it has a couple of flaws: major lack of speed and not a single weapon slot. Roboduck also has a unique feature useful in battle which allows this robot to quack.
Base speed - 5 mph
Durability - 1000000
Hardpoint slots - none
Special ability - Quack
Required account level - 31