Diamond Knight 
Artifact Creature — Knight
$0.30 #15130 0.11 7.3 years
Vigilance (Attacking doesn't cause this creature to tap.)
As this creature enters, choose a color.
Whenever you cast a spell of the chosen color, put a +1/+1 counter on this creature.
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Cards similar to Diamond Knight expected a card that isn't here?
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"Whenever you cast a spell of the chosen color, you gain 1 life."
+1 more matching line
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"As this artifact enters, choose a color."
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"As this artifact enters, choose a color."
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"As this artifact enters, choose a color."
Seal of the Guildpact79%
$0.36↑#125370.1410.9 years↑
"As this artifact enters, choose two colors."
Mage Tower Referee78%
$0.11↓#23626↓0.01↓0.5 years↓
"Whenever you cast a multicolored spell, put a +1/+1 counter on this creature."
Sisterhood of Karn78%
$0.23↓#124100.37↑3.0 years↓
"Whenever you cast a spell from anywhere other than your hand, double the number of +1/+1 counters on this creature."
Throne of Eldraine78%
$29.41↑#897↑0.28↑3.1 years↓
"As this card enters, choose a color."
Gauntlet of Power78%
$3.80↑#2627↑0.2020.0 years↑
"As this artifact enters, choose a color."
Satyr Hoplite77%
$0.13↓#21251↓0.0712.5 years↑
"Whenever you cast a spell that targets this creature, put a +1/+1 counter on this creature."
Setessan Oathsworn77%
$0.16↓#23889↓0.1112.7 years↑
"Whenever you cast a spell that targets this creature, put two +1/+1 counters on this creature."
Pheres-Band Thunderhoof77%
$0.13↓#29546↓0.0712.5 years↑
"Whenever you cast a spell that targets this creature, put two +1/+1 counters on this creature."
Staunch-Hearted Warrior77%
$0.03↓#28363↓0.00↓13.1 years↑
"Whenever you cast a spell that targets this creature, put two +1/+1 counters on this creature."
Centaur Battlemaster77%
$0.07↓#26566↓0.0613.1 years↑
"Whenever you cast a spell that targets this creature, put three +1/+1 counters on this creature."
Lagonna-Band Trailblazer77%
$0.12↓#21221↓0.0612.5 years↑
"Whenever you cast a spell that targets this creature, put a +1/+1 counter on it."