Dota Duo Combos

[Instinx]

Vengeful Spirit and Luna. Double up damage aura ftw! Also double stun is lots of fun.

[frigidhell]

Poison Nova + Fatal Bonds - for teamfights it's very strong.
Dazzle + Slardar : Very powerful defensive lane with huge punishing potential (can punish mistakes really hard).

[aetherfox]

I've seen a jungling Windrunner in the competition to get into the 2012 International, she was set to go up against an impossible trilane, she saw her opponents then abandoned the lane and went to the jungle and managed to clear 1 creep camp for 1 level then had to go heal =p

Not the first time I've seen a 4-1-0 lane set up, but probably the first time it worked out well, all depends on how quick each team adapts to it.

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I don't think there are any particularly imbalanced duos.

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Besides Dark Seer, the Invoker is another one of those heroes that has synergy with nearly any other hero in the game. Come to think of it, Invoker and Dark Seer on the same team would be pretty funny... Vac + Tornado + Meteor + Deafening Blast....

[TheMeadow]

Vengeful Spirit and Luna. Double up damage aura ftw! Also double stun is lots of fun.

Just need to throw a drow in mix too for more aura dmg fun

[revengous]

played list night with work mates

he was ursa I was drow (we stuck together the entire match)

final score:
ursa 15/x/x
drow x/x/15

still a potent combo, since drow stops you from running away from ursa

[Deux_D]

A friend of mine & I can sure stomp a lane with a Lone Druid + Witchdoctor combo. Not sure if it's at all to do with hero synergy as much as it is to do with our player synergy.