Ignus is a stage hazard from Kirby 64: The Crystal Shards, first seen in Stage 4 of Neo Star. It yields no Copy Ability when swallowed.
Ignus is little more than a chunk of volcanic rock that will rain down from the sky. It comes in three sizes. The smallest one is barely larger than a pebble, and will break immediately upon hitting the ground. The medium one is comparable to Kirby in size, and will bounce once on the ground before breaking. The large ones are bigger than Kirby, and will split into two medium Ignus when they hit the ground. Ignus will fall continuously from the sky, so it is not possible to dispose of all of them.
Ignus appears only in Neo Star - Stage 4, out in the first area that Kirby traverses. Unless Kirby wants to play with the Ignus rocks for some reason, he ought to just move along past them.
Kirby dodging several Ignus as he enters the volcano in Neo Star - Stage 4