Clamor Shaman 

Creature — Goblin Shaman
Riot (This creature enters with your choice of a +1/+1 counter or haste.)
Whenever this creature attacks, target creature an opponent controls can't block this turn.
click a line to search just that ability, click more to combine them
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.
Plasma Jockey 100%
$0.12#21759
"Whenever this creature attacks, target creature an opponent controls can't block this turn."
Radha's Firebrand 98%
$0.18#21319
"Whenever this creature attacks, target creature defending player controls with power less than this creature's power can't block this turn."
Gilded Cerodon 97%
$0.04#27831
"Whenever this creature attacks, if you control a Desert or there is a Desert card in your graveyard, target creature can't block this turn."
Goma Fada Vanguard 97%
$0.09#15871
"Whenever this creature attacks, target creature an opponent controls with power less than or equal to the number of Warriors you control can't block this turn."
Grotag Thrasher 96%
$0.11#27970
"Whenever this creature attacks, target creature can't block this turn."
Goblin Heelcutter 96%
$0.08#20211
"Whenever this creature attacks, target creature can't block this turn."
Mardu Roughrider 96%
$0.10#24229
"Whenever this creature attacks, target creature can't block this turn."
Goblin Locksmith 95%
$0.14#23691
"Whenever this creature attacks, creatures with defender can't block this turn."
Spider-Man, Web-Spinner 90%
$23.90#23672
"Whenever this card attacks, target creature can't block this turn."
Crashing Boars 88%
#29408
"Whenever this creature attacks, defending player chooses an untapped creature they control. That creature blocks this creature this turn if able."
Maulfist Doorbuster 88%
$0.10#25757
"Whenever this creature attacks, you may pay {E}. If you do, target creature can't block this turn."
Forgehammer Centurion 84%
$0.09#21835
"Whenever this creature attacks, you may remove two oil counters from it. When you do, target creature can't block this turn."
Aragorn, King of Gondor 84%
$0.73#4070
"Whenever this card attacks, up to one target creature can't block this turn. If you're the monarch, creatures can't block this turn."
Grappling Hook 83%
$1.13#9891
"Whenever equipped creature attacks, you may have target creature block it this turn if able."
Vengeful Villagers 83%
$0.10#24065
"Whenever this creature attacks, choose target creature an opponent controls. Tap it, then you may sacrifice an artifact or creature. If you do, put a stun counter on the chosen creature."
Impetuous Devils 82%
$0.27#15995
"When this creature attacks, up to one target creature defending player controls blocks it this combat if able."
Avalanche Tusker 82%
$0.16#25019
"Whenever this creature attacks, target creature defending player controls blocks it this combat if able."
Frenzied Goblin 81%
$0.24#9581
"Whenever this creature attacks, you may pay {R}. If you do, target creature can't block this turn."