Ignus is an obstacle that appears in Kirby 64: The Crystal Shards. It is a gray or dark brown igneous rock (just like its name suggests) and is found in the fourth stages of both Aqua Star and Neo Star. Ignus' only method of attack is just falling from the sky to land on Kirby. Kirby can carry an Ignus above his head to protect himself from other Ignuses. Despite being a volcanic rock itself, Ignus gives neither the Fire nor the Stone ability.
The Prima strategy guide for Kirby 64: The Crystal Shards is flawed; it mistakes Ignus for Putt's boulder, and refers to the real Ignuses as simply volcanic rocks.