An expensive last-ditch tower defense that collapses the stairs into a ramp and rolls barrels down at attackers.
All manned synergy towers follow the same rule as castles: there must be a path to the main room. Carl and Princess Donut worked around it by making that path lethal. Donkey Kong is an expensive, last-ditch defense installed inside the Nest Tower: hitting a switch makes the stairs disappear and turn into a steep ramp, down which barrels of various types begin rolling.
Activated, the interior also gains multiple magic-numbing effects — most mages are left defenseless while the barrels keep working — though Lucia Mar proved powerful enough to partially break through the anti-magic zone. Skills still function, letting Carl climb the oil-slicked ramp on Sticky Feet. Donut's barrel arsenal included oil, fire, a Sleep Potion Barrel and Mute Barrels.
A curving interior shaft turned to a steep ramp, rivulets of oil running to the bottom, the smell of fire in the air and electricity crackling in the walls.
The Nest tower's final layer of defense, buying Donut time against Lucia Mar.