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"Detain each non-land permanent that your opponent controls with converted mana cost 4 or less."

fwiw, in your last post, Lavinia shouldn't affect emrakul in anyway unless I am mistaken.

Lavinia only triggers her ability when she enters for one turn. I can see the card being good, but better than captain of the watch?

To be fair, Legionnaire is really a 2 drop. A 3/1 for 2 that first strikes is pretty big game.

Idon't think it has the maelstrom pulse ability of killing all with the same name.