[CHEESE] Lord Erebus' Mist
Untouchable
I realize this has the negative effect of him having to have enough mana to support it - but especially later game he can seemingly stay in mist forever - totally invulnerable.
Even attempts to counter (by using truesight items) proved useless - he is not invisible, but invincible. He could run up in the middle of a chokepoint with towers and do Mist - totally killing your creeps with the DPS from Mist and also regaining life at a solid rate. All the while if you try to wait him out you get crushed by people on his team - since he can wait so long.