My Legions are coming

Enchant instant card in a graveyard
Whenever you cast a sorcery spell, copy the
enchanted instant card. You may cast the copy
without paying its mana cost. If you do, exile
the enchanted card and attach My Legions are
coming to another instant card in a graveyard.
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,,No, but I’m... You can’t. It’s not. But you.
Not fair! Please."