Master Trapper Achievement
Trap 100 bunnies and/or skunks.
Since skunks spawn so rarely, this achievement is most easily accomplished on an arctic biome by trapping bunnies.
While bunnies do spawn randomly, your best bet is to find a maw that spawns mostly (or only) bunnies. Such maws usually occur closer to the surface of the world. Sometimes you can find a couple of these maws close together. Position yourself underneath and dig a hole designed to funnel the bunny into a one-block wide chute. When the bunny falls into the chute, place a dirt block directly above it so that you have only one square block with the bunny in it, then place the cage. When done correctly, the bunny will disappear, leaving a little pile of fur behind.
Another method is to wait for the bunny or skunk to pause, then quickly surround it with dirt and smack the cage down. Since these mobs don't pause for longer than a few seconds, and are able to jump through many kinds of corners, this method requires quick reflexes.
The very first arctic world, Kirkcaldy, has a bunny trapping farm set up.