Alsira, The Insidious Siren
In Shuffle Heroes some cards enable to get cards from your opponent into your deck. This way you can exploit more complex combinations.
Alsira The Insidious Siren is all about this mechanic. She can exchange cards with hers opponent or even use opponent's hero actions.
During the hero draft you should be careful to over commit to some great heroes combo because your opponent can abuse it by picking the Alsira.