Flash as a card has ruined the cEDH scene to the point where 40% of the decks you play against are Flash Hulk builds. Since the release of Thassa's Oracle ALL hulk decks have now moved in a single direction combining Breakfast Hulk, Shuffle Hulk & Sacred to now all be what's considered "Fish Hulk". 

Flash as a card combined with a 4 or 5 color commander because extremely easy to tutor for, let's not forget about transmute ability either. 

Flash

• NOT LEGAL in Standard, Brawl, Modern, Pauper & Penny
• BANNED in Legacy 
• RESTRICTED in Vintage

Why is Flash still legal in Commander? Does the RC play Flash Hulk decks and are biased? 

What's unfortunate is the cEDH scene is now littered with Flash Hulk decks... A singleton format that thrives on diversity is now in boxed into a small corner with limited variation between deck-list. 

Protean Hulk was banned before and there was reasoning behind it, however, Hulk was never the problem as the multi step setup isn't anywhere near as easy to compile. Throwing Flash in the mix makes Protean Hulk broken but more importantly it makes the cEDH format boring. 

Flash + Protean Hulk has been a pretty potent combo for a while, even for competitive. What makes the addition of Thassa's Oracle so scary is that you can do the entire line in response to the trigger, and the hulk allows you to grab a piece of protection too, and that you don't need to be holding a draw spell/trigger.

Protean Hulk dies, trigger stacks and resolves
Search for Nomads en-Kor , Cephalid Illusionist Thassa's Oracle and any 1 CMC protection creature like Siren Stormtamer .
As they enter the battlefield, the trigger for Thassa's Oracle is stacked
You hold priority, and repeatedly use Nomads en-Kor to target Cephalid Illusionist , flipping your library into your GY
Resolve the triggers above Oracle trigger. You now have no library, so when the Oracle trigger resolves it will see 2 devotion (for Oracle) being greater than 0 cards in library, and you will win the game
Holding up Siren Stormtamer for interaction
That's not even the worst possible combo. You can crack hulk for Grand Abolisher Nomads en-Kor Cephalid Illusionist and any 1 CMC creature. Flip GY, then flashback Dread Return from GY to return Oracle, saccing Nomads, Illusionist, and the 1 CMC critter. Grand Abolisher guarantees safety during combo resolution, and you don't need any more library flip after its done once.

I'm sure you can find other protection piles too. Use Spellseeker to find Silence with Nomads + Illusionist + Dread Return , although that does require using  after combo. The point remains that there is flexibility in combo protection with this little guy in play.

Think about Oracle like this. Its 1 CMC cheaper than Laboratory Maniac , and it doesn't need an additional draw trigger to win. It can still win if its removed while the trigger is on the stack, which is HUGE. The only downside is that it only checks upon ETB. This downside is pretty trivial though, as you don't wish to put the creature into play until there's an opportunity to win.

Its basically labman with a draw stapled to it for -1 mana. Normally labman + draw in a hulk package would eat 4 CMC of your 6. This only takes away 2.