When other creatures you control enter play, they gain an additional +1/+1 counter for each opponent that lost life this turn
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If it's something you can spend mana on, it's a cost
Step 3: Build the Deck I wanted to use a commander that isnt seen much as an example, so I decided to brew something around Asmoranomardicadaistinaculdacar

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You could make a pretty standard +1/+1 counter deck, or go the opposite route with -1/-1 counters