Berserk on a stick. Well, kind of.
So Gruul got the fatties you ramp for, good for them! Well, it was somewhat expected but I like what they did with the Bloodrush mechanic. It’s like an ‘Evoke/Channel’ mechanic that’s more linear. The creature will always lend it’s regular stats to an existing creature in an effort to inflict maximum damage/end the game faster (or to a lesser extent, allow you to do some combat trick and have your critters live).
Ever have those situations where ‘one more turn/attack step and you had him?’ Well, now you can drop that excuse because you can think of all these creatures as having haste as long as you control at least one other creature. So instead of dropping a 9/9 trampler and waiting for your next combat phase that may or may not come (board sweepers, removal pacifism effect) just ‘Rush’ in!
Another relevant advantage that this mechanic has: it bypasses counterspells. Yeah, remember those nasty things? They still exist in Standard despite the insane amount of Cavern of Souls decks running around. So think before you mindlessly cast this thing on your main phase: “Would it better server its purpose to attack first and see what happens first?”
Chances are that it would.