That event happened in Stronghold when, to save Mirri, Crovax was forced to kill Selenia
(You may cast this card from your graveyard for its escape cost.) Escape, Exile five other cards from your graveyard
Then if you control an untapped land, destroy all enchantments you control
"The trading system is predatory and downright greedy," wrote ACNL on Reddit, who outlined the Trade Token conversion rates
While its symmetrical effect is typically seen as a downside compared to Doubling Season, you should instead use its presence on the field to your political advantage: Dont remove me from the game, youre getting value off of my Primal Vigor, Wait, I can cast Primal Vigor next turn and we can swing in with all those Tempt with Vengeance tokens, etc