Dude, Where's My Dragon: Gwenpool Bonus Mission 3
After completing Royal Rampage and The Sorcerer's Stones, activate this one atop the medieval castle.
When the intro ends, start by smashing the heap of junk stage left.
Use the pieces to build a clock.
The clock controls when the various traps and ramps of the level are activated. Use Merlin to turn back the clock while Arthur runs the gauntlet. You may need to swap back and forth a few times to get Arthur through (do note that the spiked columns only move left/right, never toward/away from the camera).
Pass through the stage-rightmost door to trigger the next scene. Only one character has to make it- so you can leave Merlin by the clock.
Before smashing the obviously fake dragon center stage, you might take a moment to melt the gold grilles downstage left and right.
Then bust up the dragon to confront Morgan Le Fay.
Blast away a few skeletal goons (they don't even have shields), then use the dragon pieces to build a rune platform.
Solve the rune to free up red pieces, which you can build into a red throne.
Slide this stage-left as far as it can go, then use it as a trampoline to reach the upper level. It's possible to make the jump while the spiked column is spinning, but much easier when it isn't.
Slice away the alcove vines, then use magic on the contents.
This triggers an attack on Morgan, and drops two piles of pieces. Build one into a blue throne, and use the other to repair the slidey tiles. Slide the throne stage right.
As before, trampoline upward, this time to reach some acrobatic poles, which lead to an acrobatic pole switch.
This triggers the third and final phase of the fight. Best a small wave of harmless skeletons for Morgan to unleash her secret weapon.
Now you can use the pieces from underneath the gold grilles earlier. Use the leftward ones to build a giant jester cap, and then magic it into place atop the Sentry.
Use the rightward pieces to build a lute, which you can magic into song.
All you need is a single hit on the Sentry's back to end the fight.
This completes the mission, and unlocks Morgan le Fay.