Thranduil's Decree 
Instant
Counter target spell. If a permanent spell is countered this way, exile it instead of putting it into its owner's graveyard. You may cast that card without paying its mana cost for as long as it remains exiled.
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Cards like Thranduil's Decree, and the alternatives to it, ranked by how closely they do the same thing.
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.
Spelljack 95%
$1.6#16616
"Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard. You may play it without paying its mana cost for as long as it remains exiled."
Transcendent Dragon 94%
$0.37#7299
"When this creature enters, if you cast it, counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard, then you may cast it without paying its mana cost."
Kheru Spellsnatcher 88%
$0.18#7592
"When this creature is turned face up, counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard. You may cast that card without paying its mana cost for as long as it remains exiled."
Liquify 85%
$0.16#28981
"Counter target spell with mana value 3 or less. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
Dissipate 80%
$0.09#6257
"Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
Void Shatter 80%
$0.32#11986
"Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
Deny Existence 80%
$0.07#19521
"Counter target creature spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
Assert Authority 78%
$0.26#12296
"Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
Syncopate 76%
$0.13#3876
"Counter target spell unless its controller pays 
. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
No More Lies 76%
$0.32#5773
"Counter target spell unless its controller pays 
. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
Gale's Redirection 76%
$0.36#8950
"You may cast the exiled card for as long as it remains exiled, and you may spend mana as though it were mana of any color to cast that spell."
Devious Cover-Up 75%
$0.11#12728
"Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard. You may shuffle up to four target cards from your graveyard into your library."
Delay 74%
$1.8#2082
"Counter target spell. If the spell is countered this way, exile it with three time counters on it instead of putting it into its owner's graveyard. If it doesn't have suspend, it gains suspend."
Deny the Divine 73%
$0.06#19400
"Counter target creature or enchantment spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
Guile 73%
$0.83#11549
"If a spell or ability you control would counter a spell, instead exile that spell and you may play that card without paying its mana cost."
Faerie Trickery 72%
$1.13#11387
"Counter target non-Faerie spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
Horribly Awry 72%
$0.09#21798
"Counter target creature spell with mana value 4 or less. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
Spell Shrivel 71%
$0.21#16399
"Counter target spell unless its controller pays . If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
Force of Negation 70%
$47.17#266
"Counter target noncreature spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."
No Escape 70%
$0.17#16568
"Counter target creature or planeswalker spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard."