The Fungus Beetle does not spawn on its own, and requires the player to summon it with a Mushroom Crystal. The Fungus Beetle can only be summoned, anywhere at any time of the day after Brain of Cthulhu or the Eater of World has been defeated.
The Fungus Beetle flies around the player, spawning different enemies that makes the boss immune to damage while they are alive.
Will usually perform a series of rapid charges that are difficult to escape from.
Occasionally summons Great Fungus Bugs with 120 HP (240 in Expert Mode) that deal 30 damage (70 in Expert Mode). As long as one of these is alive, the Fungus Beetle is invulnerable.
Can summon groups of Little Mushroom Bugs with 100 / 200 in Expert Mode) that deal 30 / 50 in Expert Mode) and will home in on the player.
Can release Fungi Spores that drift downwards, swaying in the player's direction. These are the most dangerous threat, as they do the most damage (70 / 160).
It is recommended to fight the Fungus Beetle on an elevated platform of some sort as the Great Fungus Bugs that make it invulnerable tend to fly around below the player. This means that if you fight the Fungus Beetle at ground level it can be tricky to kill them without a weapon that can pierce through blocks, which makes it frustratingly slow to kill the Fungus Beetle.