Siege Striker 

Creature — Human Soldier
Double strike (This creature deals both first-strike and regular combat damage.)
Whenever this creature attacks, you may tap any number of untapped creatures you control. This creature gets +1/+1 until end of turn for each creature tapped this way.
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Ledev Champion 100%
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"Whenever this creature attacks, you may tap any number of untapped creatures you control. This creature gets +1/+1 until end of turn for each creature tapped this way."
Orphans of the Wheat 96%
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"Whenever this creature attacks, tap any number of untapped creatures you control. This creature gets +1/+1 until end of turn for each creature tapped this way."
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"Whenever this creature attacks, you may tap two other untapped creatures you control. If you do, this creature can't be blocked this turn."