That means it's likely that your opponents will have larger creatures, meaning they'll be drawing the cards, and that you'll only be adding two to three mana off of Selvala's ability, most times

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Lucky for the Siege-Gang, this Goblin officer is all smiles
Suddenly, it turns into a different game of reading people, doesn't it
You might think, oh, well its impossible to play that many cards in a single turn, but youd be wrong
For just four mana thats a pretty excellent rate, though it does come with several strings attached