Norn's Choirmaster 
Creature — Phyrexian Angel
$13.10 #3372 0.26 3.6 years
Flying, first strike
Whenever a commander you control enters or attacks, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
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Cards similar to Norn's Choirmaster 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.
Metastatic Evangel82%
$0.37↓#1514↑0.332.2 years↓
"Whenever another nontoken creature you control enters, proliferate."
Keleth, Sunmane Familiar82%
$0.21↓#6749↓0.00↓5.8 years↑
"Whenever a commander you control attacks, put a +1/+1 counter on it."
Atraxa, Praetors' Voice78%
$24.32↑#2475↑1.72↑9.8 years↑
"At the beginning of your end step, proliferate."
Tainted Observer77%
$0.22↓#7047↓0.47↑3.6 years
"Whenever another creature you control enters, you may pay 
. If you do, proliferate."
. If you do, proliferate."
Agent Frank Horrigan74%
$5.51↓#34800.302.5 years↓
"Whenever this card enters or attacks, proliferate twice."
Tome of Legends74%
$0.30↓#2279↑0.196.9 years↑
"Whenever your commander enters or attacks, put a page counter on this artifact."
Surge Conductor74%
$0.36↓#27510.37↑1.1 years↓
"Whenever another nontoken artifact you control enters, proliferate."
Stumpsquall Hydra72%
$0.52↓#13181↓0.12↓5.8 years↑
"When this creature enters, distribute X +1/+1 counters among it and any number of commanders."
Thrummingbird72%
$0.25↓#845↑0.2215.9 years↑
"Whenever this creature deals combat damage to a player, proliferate."
+1 more matching line
Thunder Spirit72%
$126.51↑#30468↓0.38↑32.3 years↑
"Flying, first strike"
Steeple Roc72%
$0.05↓#29772↓0.00↓13.3 years↑
"Flying, first strike"
Plover Knights72%
$0.13↓#28368↓0.2418.9 years↑
"Flying, first strike"
Battlefield Raptor72%
$0.26↓#7952↓0.245.6 years↑
"Flying, first strike"
Sabertooth Wyvern72%
$0.09↓#31828↓0.53↑28.2 years↑
"Flying, first strike"
Silverclaw Griffin72%
$0.19↓#26587↓0.3314.6 years↑
"Flying, first strike"
Voiceless Spirit72%
$0.07↓#28289↓0.2114.9 years↑
"Flying, first strike"
Sky Spirit72%
$0.16↓#28459↓0.00↓28.9 years↑
"Flying, first strike"
Ekundu Griffin72%
$0.10↓#24650↓0.2929.9 years↑
"Flying, first strike"
Angel of Retribution72%
$0.22↓#27003↓0.2124.6 years↑
"Flying, first strike"
Skyhunter Patrol72%
$0.04↓#22884↓0.2722.9 years↑
"Flying, first strike"