They are found on the Bomb Floor, a Dwarven-like floor of the Lunar Ruins filled with Bomb-type monsters. All enemies have field sprites, and coming into contact with them will trigger a battle. The Melt Bomb field sprite looks like a dark Bomb engulfed in fire, randomly popping out from the lava and passing over the path.
It always appears by itself, and it only has one attack, Self Destruct. Since it has 9,999 HP, it can easily KO one party member if the party has been ambushed by it. It does not give any experience or money when defeated, and the party cannot escape from it, leaving little choice but to kill it as quickly as possible, or minimize Self-Destruct's damage at the least.