The Beyonder is a more pure plot element. Q shows far more fallibility (is one of many in his race, is stripped of his powers at one point, etc). Q has more character development, but clearly the Beyonder in this face off.The Beyonder vs. Q. Discuss.
Meanwhile hidden beneath the mortal lands, the most intelligent and cunning being left in the multiverse coordinate and scheme. They wait until all is settling and their enemies are at their weakest. Then the Elder Brains and their illithid children arise to take over the world...
I thought you were going for aboleths, but this will work.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.