Ugh, don’t bring that up again.

It’s really simple: one chonky bear converts to 4 lynxes, which weigh 17 raccoons, which in turn weigh exactly 7 armadillos, that come down to 638 roaches.

Upwards conversion is just as easy: one chonky bear is exactly 1/3 of a Swasticar, which converts to 2/7 of a large boulder the size of a small boulder.