Take Maw or Nydus and it's respective levle 20 upgrade... they are situational... I tend to lean Nydus since they're great perma-wards, lane control, and useful to block pathways.

The rest is written in stone for it lets you get camps, demolish heroes... and as the game progressives your autoattacks get mad deadly... Nydus helps a lot with this build for the amount of mana it consumes... thus why I lean Nydus unless the map/matchup demands maw.

Use Nydus in the Mines on Haunted mines perhaps... get a lot of skulls fast.