This article is from the X-Men Comic Books FAQ, by Kate the Short (firstname.lastname@example.org) with numerous contributions by others.
What happens when the unmovable object meets the irresistible force? In
this case, it's easy. Magic, in the case of Juggernaut, wins. The Blob
is merely very, very difficult to move, not impossible. Juggernaut's
unstoppability, on the other hand, derives from the Crimson Gem of
Cyttorak. As magic, it can't be defeated by mutant powers.