I've been keeping track for awhile of the decks I used against FGs and the win record. This deck is 5-1 against Obliterator: (I think it was developed by majofa in his anti-FG series)
Hover over cards for details, click for permalink
6ts 6ts 6ts 6ts 6ts 6ts 6ts 6ts 6ts 6tt 6tt 6tt 6tt 6tv 6tv 6u7 6u7 6u7 6u7 6u7 6u7 6ve 6ve 6ve 6ve 80h 80h 80h 80i 80i 8pu
Don't play a dragon until you can fractal it because of the gravity pulls. Try to save antimatters for the dragons since the demons can kill the shriekers. I have some purple nymphs, but this deck is actually quite quanta starved so I haven't tried using them.
Due to the pulverizer, I wouldn't recommend a rainbow deck (unless it didn't rely on permanents) or instosis. Instosis probably has an okay record against obliterator, but it won't be as good as this deck. My rainbow control deck can pwn obliterator -if- he doesn't get an early pulvy, but if he does, it's usually doomed.
SPlat might work here, but I've never tried it. Just remember that shriekers will burrow against SoSa.