Dark Willow + Spectre

Why this works

Jumping on a lone hero with Haunt becomes a much safer kill attempt when Dark Willow is on the map. Spectre has no stun of her own, so targets can often escape before she secures the kill. Dark Willow provides the missing piece with Cursed Crown or Bramble Maze, holding an enemy in place long enough for Spectre's damage to stick. The control from Willow lets Spectre get more attacks on an isolated hero, which is exactly where her damage comes from.

This combo gives the team a way to punish split-pushing or out-of-position supports all through the mid-game. Once Spectre has her ultimate, the two can coordinate to find picks and accelerate her farm. The challenge is that Dark Willow isn't global, so she has to anticipate where a fight will happen to be effective. An enemy team that sticks together can make it much harder for Spectre to isolate a target, reducing the effectiveness of Willow’s follow-up and forcing a more traditional teamfight.