If you're new to mid or already high-ranked this may not be the best call, but if you have no morals or soul just learn Diana. If you survive until 6 (not too hard with a shield and low cost poke), you kill the other guy. Her ult is one of the most toxic moves in the game imo (and I mained her for most of her existence), being a double gapclose with a .6 ap ratio each. 1 passive and a QRR comes out to 2.5x ap (anivia's burst) and the only skillshot is the first Q. Offtank her and you can delete any character on the enemy team then live long enough to use passives and spammable cd's to mop up. Not saying you can 1v5, but some beef and zhonyas post-burst can let your team follow and turn you into a tanky magic burst dps initiator assassin.
Edit: Also, she benefits from early durability enough to stop assassins from killing her but still has the damage to kill them when they realize the all-in failed.