Void Mirror 
Artifact
$0.39 #15623 0.89 5.5 years
Whenever a player casts a spell, if no colored mana was spent to cast it, counter that spell.
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Cards similar to Void Mirror 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.
Vexing Bauble96%
$2.98↑#1297↑0.802.3 years↓
"Whenever a player casts a spell, if no mana was spent to cast it, counter that spell."
Lavinia, Azorius Renegade89%
$0.27↓#3214↑1.10↑7.7 years↑
"Whenever an opponent casts a spell, if no mana was spent to cast it, counter that spell."
Boromir, Warden of the Tower89%
$4.45↑#874↑0.64↓3.3 years↓
"Whenever an opponent casts a spell, if no mana was spent to cast it, counter that spell."
Ice Cave86%
$0.74↑#21369↓0.8225.4 years↑
"Whenever a player casts a spell, any other player may pay that spell's mana cost. If a player does, counter the spell."
Planar Chaos80%
$2.33↑#7172↑1.35↑24.4 years↑
"Whenever a player casts a spell, that player flips a coin. If they lose the flip, counter that spell."
Chalice of the Void78%
$16.39↑#9424↑1.14↑23.0 years↑
"Whenever a player casts a spell with mana value equal to the number of charge counters on this artifact, counter that spell."
Nix76%
$0.98↑#25782↓0.06↓19.5 years↑
"Counter target spell if no mana was spent to cast it."
Nether Void75%
$673.40↑#163262.18↑32.4 years↑
"Whenever a player casts a spell, counter it unless that player pays 
."
."
Presence of the Master74%
$0.55↑#26381↓1.30↑32.4 years↑
"Whenever a player casts an enchantment spell, counter it."
Roiling Vortex72%
$1.36↑#2588↑0.54↓6.1 years
"Whenever a player casts a spell, if no mana was spent to cast that spell, this enchantment deals 5 damage to that player."
Hesitation72%
$0.31↓#23370↓0.60↓28.6 years↑
"When a player casts a spell, sacrifice this enchantment and counter that spell."
Bazaar of Wonders72%
$2.60↑#28491↓0.38↓30.0 years↑
"Whenever a player casts a spell, counter it if a card with the same name is in a graveyard or a nontoken permanent with the same name is on the battlefield."
Chancellor of the Annex71%
$3.18↑#10165↑1.43↑15.4 years↑
"Whenever an opponent casts a spell, counter it unless that player pays 
."
."
Lunar Force70%
$0.28↓#21452↓0.35↓10.2 years↑
"When an opponent casts a spell, sacrifice this enchantment and counter that spell."
Counterbalance70%
$2.51↑#3414↑1.00↑20.2 years↑
"Whenever an opponent casts a spell, you may reveal the top card of your library. If you do, counter that spell if it has the same mana value as the revealed card."