Varian is "Overextend: The Card"
Overextending is only a problem in control mirrors. Priests (Lightbomb), Paladins (Equality Combos), and Warriors (Brawl) can punish you hard, but Druids and Hunters can't do shit about a Varian that pulls two to three other big bodies onto the field. Warlocks can potentially blow you up with a Shadowflame combo and Rogues can clear with an Oil + Blade Flurry combo, but not every Warlock is Handlock and Rogues aren't that common right now. Freeze Mage can board wipe you, even if it takes several turns with Blizzard followed by Flamestrike the next turn, but Tempo/Flamewaker Mages are way more common. Even Mech Mage is more common on ladder than Freeze. But even if it is a Freeze Mage, you should've already won just by playing Justicar. A lot of Shamans can't really punish you for it, either. Elemental Destruction is the only card that has a chance at board wiping you, and that might not even do it depending on what you pulled and doesn't make it into most of the current Aggro Shamans anyway. When I was running Varian, my biggest problem was the cost. If I was playing against Face Hunter or Aggro Druid, I couldn't afford to spend 10 mana on anything that didn't add health/armor. And pulling Shield Maiden or Justicar without the battlecry could cost you the match. In control matchups, Varian could cause you to lose to fatigue and those are the match ups where overextending can cost you. He's just too slow to counter aggro and he overextends you in control mirrors. That being said, I did have some crazy wins where I played Varian and he pulled Geddon which set up lethal next turn with Alex's battlecry. Or Varian top dicking Grom when I had Death's Bite already equipped for lethal.