Arch-lichen are extraordinarily hard to kill due to their numerous resistances and good AC. They also have reflection and can split in two if the player somehow manages to bypass their -78 AC with a melee weapon. On the Astral Plane, up to 10 pre-placed arch-lichen will be encountered, and there may also be one in Moloch's Sanctum waiting to ambush unwary players.
By applying the Arch-lichen patch, the following true rumor will be added:
They say RNG hath made that which was weakest the greatest of all.
Arch-lichens, or Fwagglebrapo in Quenya, are a deadly race
of... things. They were first fwapped into creation by the
omnipotent RNG for the sole purpose of executing overtly lucky
adventurers. In His omnipotence, however, the RNG discovered
that he had made a creature that even He cannot kill. Naturally,
it follows that no divine intervention can protect an adventurer
from the wrath of an arch-lichen.