Crystal Maiden + Ogre Magi

Why this works

Having an Ogre Magi on your team who can always afford his spells is a nice bonus. Crystal Maiden's Arcane Aura keeps his mana topped off, which is a big deal for a hero with an expensive kit. This means he can use Ignite more freely to harass in lane and, more importantly, keep Bloodlust active on a core without worrying about running dry. Ogre Magi gets to play a more aggressive, spell-heavy game, while Crystal Maiden supports from a safe distance, enabling him to be a constant nuisance from the start.

This pressure can make the laning stage very difficult for the opposition, with constant slows and stuns wearing them down. Later, the reliable mana for Ogre means more consistent uptime for Bloodlust during pushes and teamfights. The advantage is only a slight one, though. Both heroes are slow and lack escapes, making them prime targets for ganks. An enemy team with good initiation can often pick one or both of them off before the sustained spell-casting becomes a factor, which prevents the duo from consistently taking over a game.