Lava Slime

The Lava Slime was added in the 1.0.5 patch and spawns in the underworld. It gives off an orange glow like Molten armor.

When killed it melts into lava, which can do a serious amount of damage to the player if he/she does not get out of the way. It also does not receive damage from lava; in fact it floats in it like other slimes float in water.

It is suggested to kill Lava slimes with a ranged weapon - that is, if you wish to kill them at all. The problem is, they drop literally nothing but Lava. No items... no Gel... no coins. Couple this with the fact that they do very little damage while alive - especially if you are wearing Molten Armor and/or using Ironskin Potions, it may be wise to just avoid them as best you can.