River Heralds' Boon 
Instant
$0.06 #24682 0.38 8.9 years
Put a +1/+1 counter on target creature and a +1/+1 counter on up to one target Merfolk.
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Cards similar to River Heralds' Boon expected a card that isn't here?
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Jade Bearer89%
$0.06#224770.25↓8.6 years
"When this creature enters, put a +1/+1 counter on another target Merfolk you control."
Jade Guardian88%
$0.17↑#253470.65↑8.9 years
"When this creature enters, put a +1/+1 counter on target Merfolk you control."
Deeproot Elite86%
$0.28↑#5868↑0.24↓8.6 years
"Whenever another Merfolk you control enters, put a +1/+1 counter on target Merfolk you control."
Vineshaper Mystic84%
$0.16↑#236590.21↓8.9 years
"When this creature enters, put a +1/+1 counter on each of up to two target Merfolk you control."
Wanderwine Hub76%
$0.83↑#13800↑0.05↓18.9 years↑
"As this land enters, you may reveal a Merfolk card from your hand. If you don't, this land enters tapped."
Swift Warden72%
$0.19↑#209620.358.6 years
"When this creature enters, target Merfolk you control gains hexproof until end of turn."
Namor, Scourge of the Seas71%
$0.77↑#18854↑0.00↓0.2 years↓
"Each other Merfolk you control with a +1/+1 counter on it has flying."
Kopala, Warden of Waves70%
$0.28↑#4150↑0.318.9 years
"Abilities your opponents activate that target a Merfolk you control cost 
more to activate."
more to activate."
Deepchannel Duelist70%
$0.27↑#17110↑0.00↓0.6 years↓
"Other Merfolk you control get +1/+1."
Kumena's Speaker70%
$0.24↑#220670.00↓8.9 years
"This creature gets +1/+1 as long as you control another Merfolk or an Island."
Deeproot Waters70%
$0.26↑#4363↑0.378.9 years
"Whenever you cast a Merfolk spell, create a 1/1 blue Merfolk creature token with hexproof."
River Sneak70%
$0.21↑#13661↑0.418.9 years
"Whenever another Merfolk you control enters, this creature gets +1/+1 until end of turn."