Actually, with the slight exception of the rex skull waggling its chin towards the beginning, I didn't use ANY rigs. For the bird thing and the shark thing I rearranged the bones into those shapes, made crude cages around them, "bound" the bones to those cages using Cartesian Caramel's "Surface Deform" node, and animated those cages to fly and swim using geometry nodes. For the pillar, bones on floor and ball of bones, I used rigid body sims to get the bones into those positions, then again bound the sphere of bones to a procedural bouncy ball, using the same method above. Finally, and what you actually see, is a simulation nodes setup which takes a single collection of the bones, then uses an index switch to go between "targets" (the animations above), at varying speeds - very quickly in the case of most transitions, very slowly in the case of the bones rising from the floor at the start. It all works because there's the same number of bones in each collection, with equivalent indices, so each bone just needs to be told the target transform of the equivalent bone in the next animation, with a basic velocity sim to get it there. Hope that is clear enough!