Rainbow Slime

The Rainbow Slime is a hardmode enemy that spawns in The Hallow. It constantly changes color, as do the Rainbow Bricks it drops.

The Rainbow Slime requires unique spawning conditions. It will only spawn outside The Hallow biome while it is raining or during a blizzard, but only when the player is physically within a hallowed biome. In other words, it does not spawn directly on hallowed blocks, but instead spawns on non-hallowed blocks such as normal grass or snow. These conditions make it a somewhat rare monster.

Tips

 * One way to encounter Rainbow Slimes in the hallowed forest biome is to set up a Water Candle inside the edge of the hallowed biome and wait at this location until it rains, allowing enemies to spawn off screen on non-hallowed blocks. Alternatively, hallowed blocks can be covered with snow or bricks of some kind to allow Rainbow Slimes to spawn, though this will prevent other Hallow enemies from spawning.
 * Another way is to place about 200 blocks of pearlstone or pink ice above forest surface and wait for the rain with the Water Candle and Battle Potion ready. To avoid Forest transformation to Hallow, a proper spacing is required.