Opal Archangel {4}{W}
Enchantment
When an opponent casts a creature spell, if this permanent is an enchantment, it becomes a 5/5 Angel creature with flying and vigilance.
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Cards that do something similar expected a card that isn't here?
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Opal Guardian 85%
$0.19#30162
"When an opponent casts a creature spell, if this permanent is an enchantment, this enchantment becomes a 3/4 Gargoyle creature with flying and protection from red."