So, what are some fun, broken or crazy things we can do with a Mimic Vat? Well, the list is nigh-infinite, as pretty much anything with an "enter the battlefield" trigger is a ripe target. But here are some of my all-time favorites:
10. Avenger of Zendikar - Anything that makes a small army of tokens will suffice, but the Avenger is probably the cream of the crop here. It makes a shit-ton of tokens AND if you hold your land-drop until after you Vat, it pumps up those tokens as well. The best part is that when the Avenger self-exiles at EOT, the tokens stick around.
9. Blightsteel Colossus -
8. Clone - Why Imprint one just one guy on the Vat? With a Clone, you get a veritable cornucopia of things to choose from... the best thing on the board, or the most relevant utility guy... Copying a different guy every turn can be pretty tech on a crowded battlefield. Then, once someone Wraths, and there aren't any more good Clone-targets? Well, just take your pick from all the stuff that just died!
7. Karmic Guide - Repetable graveyard abuse is fun, and powerful. I like Geth a lot. I like this too.
6. Eternal Witness - This probably shouldn't be so far down on the list, but it's often more utilitarian in function than some of the stuff above it. So while it might be a tad more powerful than a few of the higher-ranked choices, it's not quite as exciting or fun... but that does depend a bit on what you get back with it...
5. Duplicant - Imprinting the Vat with and Imprint creature? What is this Nolan-esque bullshit? It's a repeatable Exile effect, that's what! Duplicant is my all-time favorite removal spell in EDH. It's colorless, so any deck can play it. It's "Exile" not "Destroy", which is just infinitely better in EDH. And it doubles as a warm body, so it can attack and block. So it's no surprise that it just gets that much better when you can make a copy every turn.
4. Puppeteer Clique - The only thing better than robbing an opponents graveyard and beating them in the face with their own guys is when their guy gets Exiled when your done with it, so they don't get it back. Some people use Withered Wretch to empty graveyards... this is way more fun.
3. Angel of Despair - There are a wide variety of creatures with "187" abilities, but vindicate-on-a-stick is much less common, and on a 5/5 flying body, this Angel is pretty much the queen of 187s. Ulamog would displace her, if not for his anti-synergy with the Vat... you won't get his trigger off the tokens.
2. Mulldrifter - Anything that draws cards is golden in my book, and this could easily be Arcanis or something similar. I chose Mulldrifter though, because it has Evoke which gives this guy a built-in way to get him Imprinted onto the Vat.
1. Primeval Titan - Obv! This guy is nuts by himself, but repetable haste-y tokens, fetching up four lands a turn is pretty damn hard to beat. Because I love drawing cards so damn much, you know it has to be something special to knock Mulldrifter off the top spot... this certainly fits that criteria.
I'm sure I'm missing about 1,000 really awesome things that you can do, but these are just my personal favorites. Feel free to leave your suggestions in the comments. I'd love to discover some new tech.