I've been having a lot of fun with the following transformational sideboards, just using Caleb Durward's stock list.

Beatdown/Discard SB:
4 Bitterblossom
4 Umezawa's Jitte
4 Dark Confidant
3 Snapcaster Mage

Snapcaster could be something better, but a lot of decks are ill-prepared to handle a stream of faeries, or Confidant's CA. Jitte makes everything a real threat. You cut all of the Goryo's, all of the fatties, entombs, and 2 shallow grave. I could see running Phyrexian Negator if you had Texas-sized balls.

I also like this sideboard

Storm Combo
4 Cabal Ritual
4 Lion's Eye Diamond
4 Infernal Tutor
1 Ad Nauseam
1 Ill-Gotten Gains
1 Chain of Vapor

This sideboard looks like it would work even better for Jacob Kory's list from Vegas. You cut mostly the same cards above, after which your deck looks like only slightly goofy Storm. Good versus GY hate, not great versus counterbalance.