I've been GMing a Golden Age Champions campaign for the last year and a half and I have found the Duplication power to be one of my best friends. Here are some examples of the fun I've had:
1) "i squared" Standard Duplicating Villain, except when a duplicate is separated from its other clones for an extended period of time it becomes an independent entity.
2) "malevolent millicent" futuristic segmented insect creature, each segment is treated as a duplicate and can function independently (attack separately) etc., similar to the hydra's head idea
3) 'the rising sun", you think they are just four ninjas until they combine into a flaming dragon (dragon is base character with four ninja duplicates, dragon dissappears when duplicates are created)
4) "?" Gladiator with sword and net who creates a mental duplicate of himself, the duplicate appears the same but is completely desolid, however all damage feedbacks to the original, the sword functions as an Ego Attack and the net as a Mental Entangle.
5)"Odin", well you know who he is,; he has a spear named Grungir which is supposed to always hit it's target. I figured it would be dumb to just have it always hit in terms of the game, so this is the solution I came up with. Odin throws the spear, if it hits, then fine. If he misses then the spear becomes a duplicate (independent character) and flys around trying to do a move through on its original target until it finally hits it; it then flies back into Odin's hand.
Well, there's mine. Anybody else?