Beastmaster's Magemark 

Enchantment — Aura
Enchant creature
Creatures you control that are enchanted get +1/+1.
Whenever a creature you control that's enchanted becomes blocked, it gets +1/+1 until end of turn for each creature blocking it.
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Cards that do something similar expected a card that isn't here?
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Guardian's Magemark 100%
$0.09#23428
"Creatures you control that are enchanted get +1/+1."
+1 more matching line
General Marhault Elsdragon 88%
$0.29#7986
"Whenever a creature you control becomes blocked, it gets +3/+3 until end of turn for each creature blocking it."
Elvish Berserker 86%
$0.11#23232
"Whenever this creature becomes blocked, it gets +1/+1 until end of turn for each creature blocking it."
Sparring Golem 86%
$0.17#30160
"Whenever this creature becomes blocked, it gets +1/+1 until end of turn for each creature blocking it."
Berserk Murlodont 84%
$0.17#27157
"Whenever a Beast becomes blocked, it gets +1/+1 until end of turn for each creature blocking it."
Rabid Elephant 81%
$0.15#28607
"Whenever this creature becomes blocked, it gets +2/+2 until end of turn for each creature blocking it."
Gang of Elk 81%
$0.27#27370
"Whenever this creature becomes blocked, it gets +2/+2 until end of turn for each creature blocking it."