Muddle, the Ever-Changing 


Legendary Creature — Elemental Otter Shapeshifter
Whenever you cast an instant or sorcery spell, Muddle becomes a copy of up to one target nonlegendary creature you control until end of turn, except it has myriad. (Whenever it attacks, for each opponent other than defending player, you may create a token copy that's tapped and attacking that player or a planeswalker they control. Exile the tokens at end of combat.)
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Cards that do something similar expected a card that isn't here?
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Bill Potts 86%
$0.18#22529
"Whenever you cast an instant or sorcery spell that targets only this card or activate an ability that targets only this card, copy that spell or ability. You may choose new targets for the copy. This ability triggers only once each turn."
Thousand-Year Storm 85%
$1.37#1394
"Whenever you cast an instant or sorcery spell, copy it for each other instant and sorcery spell you've cast before it this turn. You may choose new targets for the copies."
Leyline of Resonance 84%
$0.98#5505
"Whenever you cast an instant or sorcery spell that targets only a single creature you control, copy that spell. You may choose new targets for the copy."
Sevinne, the Chronoclasm 84%
#19831
"Whenever you cast your first instant or sorcery spell from your graveyard each turn, copy that spell. You may choose new targets for the copy."
Galvanic Iteration 83%
$0.26#2918
"When you next cast an instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy."
Pigment Wrangler // Striking Palette 83%
$0.10#18650
"When you next cast an instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy."
Doublecast 83%
$0.21#11121
"When you next cast an instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy."
Howl of the Horde 83%
$0.24#13504
"When you next cast an instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy."
Teach by Example 83%
$0.12#7586
"When you next cast an instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy."
The Mirari Conjecture 83%
$0.30#12472
"Until end of turn, whenever you cast an instant or sorcery spell, copy it. You may choose new targets for the copy."
Orvar, the All-Form 83%
$3.15#5496
"Whenever you cast an instant or sorcery spell, if it targets one or more other permanents you control, create a token that's a copy of one of those permanents."
Double Vision 83%
$0.60#2668
"Whenever you cast your first instant or sorcery spell each turn, copy that spell. You may choose new targets for the copy."
Chandra, Hope's Beacon 83%
$2.62#4076
"Whenever you cast an instant or sorcery spell, copy it. You may choose new targets for the copy. This ability triggers only once each turn."
Swarm Intelligence 82%
$0.39#4549
"Whenever you cast an instant or sorcery spell, you may copy that spell. You may choose new targets for the copy."
Splashy Spellcaster 82%
$0.18#21956
"Whenever you cast an instant or sorcery spell, create a Sorcerer Role token attached to up to one other target creature you control."
Melek, Izzet Paragon 82%
$0.13#7208
"Whenever you cast an instant or sorcery spell from your library, copy it. You may choose new targets for the copy."
Unbound Flourishing 82%
$2.17#2696
"Whenever you cast an instant or sorcery spell or activate an ability, if that spell's mana cost or that ability's activation cost contains {X}, copy that spell or ability. You may choose new targets for the copy."
Bonus Round 82%
$9.04#4815
"Until end of turn, whenever a player casts an instant or sorcery spell, that player copies it and may choose new targets for the copy."
Gale, Waterdeep Prodigy 81%
$0.48#5161
"Whenever you cast an instant or sorcery spell from your hand, you may cast up to one target card of the other type from your graveyard. If a spell cast from your graveyard this way would be put into your graveyard, exile it instead."