Gigantoplasm 

Creature — Shapeshifter
You may have this creature enter as a copy of any creature on the battlefield, except it has "{X}: This creature has base power and toughness X/X."
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Cards that do something similar expected a card that isn't here?
Reports become test cases the matcher is graded against before an update ships. Delvefall isn't a chatbot guessing, it compares the printed rules text of every card with plain math, and examples like yours decide which differences should count.
Stunt Double 96%
$4.51#3870
"You may have this creature enter as a copy of any creature on the battlefield."
Naga Fleshcrafter 96%
$0.33#5377
"You may have this creature enter as a copy of any creature on the battlefield."
Clone 96%
$0.63#3831
"You may have this creature enter as a copy of any creature on the battlefield."
Auton Soldier 95%
$10.83#2016
"You may have this creature enter as a copy of any creature on the battlefield, except it isn't legendary, is an artifact in addition to its other types, and has myriad."
Undercover Operative 94%
$0.37#5367
"You may have this creature enter as a copy of any creature on the battlefield, except it enters with a shield counter on it if you control that creature."
Jwari Shapeshifter 92%
$3.79#10849
"You may have this creature enter as a copy of any Ally creature on the battlefield."
Progenitor Mimic 92%
$1.38#5243
"You may have this creature enter as a copy of any creature on the battlefield, except it has "At the beginning of your upkeep, if this creature isn't a token, create a token that's a copy of this creature.""
Omni-Changeling 91%
$0.31#6806
"You may have this creature enter as a copy of any creature on the battlefield, except it has changeling."
Quicksilver Gargantuan 91%
$0.57#17827
"You may have this creature enter as a copy of any creature on the battlefield, except it's 7/7."
Vizier of Many Faces 91%
$0.30#4322
"You may have this creature enter as a copy of any creature on the battlefield, except if this creature was embalmed, the token has no mana cost, it's white, and it's a Zombie in addition to its other types."
Vesuvan Doppelganger 90%
#16958
"You may have this creature enter as a copy of any creature on the battlefield, except it doesn't copy that creature's color and it has "At the beginning of your upkeep, you may have this creature become a copy of target creature, except it doesn't copy that creature's color and it has this ability.""
Synth Infiltrator 89%
$0.25#8793
"You may have this creature enter as a copy of any creature on the battlefield, except it's a Synth artifact creature in addition to its other types."
Clever Impersonator 89%
$4.84#1275
"You may have this creature enter as a copy of any nonland permanent on the battlefield."
Pirated Copy 89%
$7.51#8155
"You may have this creature enter as a copy of any creature on the battlefield, except it's a Pirate in addition to its other types and it has "Whenever this creature or another creature with the same name deals combat damage to a player, you draw a card.""
Sakashima's Student 89%
$24.41#3600
"You may have this creature enter as a copy of any creature on the battlefield, except it's a Ninja in addition to its other creature types."
Mirrorhall Mimic // Ghastly Mimicry 88%
$1.19#4100
"You may have this creature enter as a copy of any creature on the battlefield, except it's a Spirit in addition to its other types."
Phyrexian Metamorph 87%
$2.32#306
"You may have this creature enter as a copy of any artifact or creature on the battlefield, except it's an artifact in addition to its other types."
Activated Sleeper 86%
$1.54#8499
"You may have this creature enter as a copy of any creature card in a graveyard that was put there from the battlefield this turn, except it's a Phyrexian in addition to its other types."
Dack's Duplicate 86%
$0.43#10875
"You may have this creature enter as a copy of any creature on the battlefield, except it has haste and dethrone."