Mainly 3 groups actually.
Firstly, Group B.
Group B
Game 1 Byzantium 2 Flash vs YellOw[ArnC]
Game 2 Medusa JangBi vs Bul_T
Winner Destination
Loser Destination
Final 아테나2
Bul_T performed SO well in his MST group I think it will be really cool to see him face up against these veterans. YarnC showed great play vs Midas in the OSL on Plasma so I think he may put up a good fight vs Flash. But the 2 possible mus I'm really looking forward too are Bul_T vs Flash or JangBi vs Flash. JangBi being the PvT beast he is and already having snagged a victory against Flash in the past will make this an exciting match. Bul_T vs Flash because I think it's interesting to see this new talent thrust into the Lion's Den and I'm excited to see how he copes.
Group C
Game 1 Medusa Jaedong vs go.go
Game 2 Destination UpMagiC vs FrOzean
Winner Athena 2
Loser Athena 2
Final Byzantium 2
This group has the potential to have such exciting games, if just for the fact we get to see Jaedong ravage some terrans. But anythings possible. UpMagic seems to be in decent form and is always very creative no matter the MU so I think he may provide some entertaining games!
and finally
Group H
Game 1 Destination Hwasin vs fantasy
Game 2 Athena 2 Tempest vs RuBy
Winner Byzantium 2
Loser Byzantium 2
Final Medusa
Group H, oh man this group is stacked. fantasy, without a doubt, will advance but we get to see Tempest in his best MU when he was a amatuer. Let's just say this. The guy can max in no time and has some of the best macro I've ever seen. RuBy and Hwasin will make interesting games of course. Really this is the group I'm most looking forward too.
Group H we get to see the new terran prodigy, fantasy, showcase even more of his brilliant TvT and we get to see Tempest butt heads with some true gosu players.
With all this said, I believe this group could be the biggest group for an upset. The main upset in my mind is RuBy destroying everyone (including fantasy) and Tempest after being down 0-1 powering through Hwasin/fantasy.
That being said, I think this is definitely the most exciting MSL we've had in a while.
Thanks for reading my rambling!