I don't know if Elrond is a game changer or breaker but he's got some solid utility that could make him easily at home with many decks that are or splash blue
The power of Meddling Mage was undeniable, especially as it came after the introduction of one-drop discard effects like Duress and Ostracize that let you look at someone's hand the turn before you could cast this
Wound Reflection, Warlock Class, Bloodletter of Aclazotz, and anything worded like this doubles your damage, which is sometimes enough to one-shot players with commanders like Heartless Hidetsugu or Alpharael, Stonechosen
This is especially the case with Charizard ex decks, which have come back into the meta with the release of Dusknoir in Shrouded Fable
I kind of want to see what stacking that deck with battle cry and myriad cards does
4 Brine Elemental Quite The Pickle Brine Elemental's one of the most devastating morphs you can have flipped face-up against you, as evidenced by the fact that its morph cost is more expensive than the actual casting cost