A salvaged gnomish Drop Bear biplane Carl repurposes and renames to fly up and board Commandant Kane's floating house.
The Nightmare II is a gnomish Drop Bear biplane — a scrap-built, barely-airworthy warplane originally named "Death Trap" (with four bombs painted on the nose) — that Louis Santiago and Langley salvage intact and stash under a tarp. Carl fuels it a quarter-full with his hoarded gasoline for lightness, spray-paints over its old name, and rechristens it "Nightmare II" after his beloved lost first-floor... (his old ride, the Nightmare). With no runway, he uses its emergency recovery balloons to float it five kilometers up to the bubble's ceiling, then pumps its engines and rudder to skitter along the top toward Commandant Kane's flying house, docking against the huge magic balloon so he and Princess Donut can climb down the net and board.
Simpler to fly than the original Nightmare, it's Carl's ticket to the last castle.
A rickety, scrap-metal gnomish biplane with a rabid-koala 'drop bear' painted on the nose, twin engines, and deployable chemical recovery balloons; freshly tagged 'Nightmare II.'
Carl's improvised aircraft for boarding the last flying castle.