Scolex appeared in the original The Binding of Isaac.
Scolex is the only Boss to have lost access to a Champion variant in an update. Specifically in Repentance, where his dark grey counterpart is inaccessible unless using Console commands to summon it.
Scolex can be considered an older or younger version of Pin, but not a posthumous one (that title goes to The Frail).
Compared to the original Binding of Isaac, Scolex's head and tail attacks are swapped.
Scolex bears some resemblance to a mythological Mongolian Death Worm, which are described as long, scaly, and blood red. It also raises half its body out of the sand and covers its prey with a lethal acidic substance, which is somewhat similar to Scolex's head attack.
Bugs[ | ]
Bug!
When Scolex is slowed, some of his body parts may detach or won't even show up - they will only be visible while entering the ground (especially the tail).
Bug!
If the final vulnerable segment of Scolex's tail is destroyed using the Chaos Card, the boss will glitch and become harder to kill. The tail will appear again if his head gets bombed or he hits Isaac.
Bug!
If you petrify Scolex (with Mom's Contacts or other similar items) when it is in mid-air, you can damage any segment of its body.
Bug!
If you fire immediately upon entering the Boss Room, rarely, you can damage Scolex before it emerges.
Bug!
If Scolex is under the effects of Broken Modem in mid-air, his jump will be stopped and he will fall.
Bug!
If Scolex is frozen with Midas' Touch or Dad's Ring and attacked, he can split into two halves, one with his head and one with his tail.