Varian, independently from the Build used, is countered by Heroes who are able to kite him due to their range (such as Hanzo who can also use Sonic Arrow to deny a flank) and/or Heroes that have tools to drastically compromise his already low mobility (such as Garrosh).

Taunt Build is countered by Heroes who have a tool to remove his Taunt (such as Anduin with Leap of Faith) and/or that have something to counter the burst damage that will come from his team (like Uther because he provides Armor to allied Heroes via Devotion).

Colossus Smash Build is countered by Heroes that have something to mitigate the burst damage that will come from him and his team (for example Medivh because Force of Will provides Protected, a status effect that has no direct counters).

Twin Blades Build heavily suffers from Heroes that can reduce his Attack Speed, crowd control him, and/or burst him down. Blinds are good against him as well.