Two enemies that appear in the medieval levels are frogs (when they collide with Crash and kiss him, it's revealed that they were princes cursed by magic) and wizards (that fire magic at Crash, which turn him into a frog if he collides with it). It stands to reason that these wizards are the reason the princes have all been turned into the various frogs, that inhabit the levels, in the first place. On closer inspection, the princes and the wizards both resemble the scientists of the previous two games (that this game reveals are basically cloned in the secret warp room). Cortex's allies are basically turning on each other, it's no wonder he's never successful.
The 100% ending. Cortex and Tropy are turned into babies, sitting in the middle of a chunk of land with gas spewing up from the craters, and with the background of the warp hole; in other words, nowhere. Though they still manage to make it funny by having them fighting over Uka Uka in a tug-of-war.