Whenever Momentum Rumbler attacks, if it doesn't have first strike (This creature deals combat damage before creatures without first strike.), put a first strike (This creature deals combat damage before creatures without first strike.) counter on it.
Whenever Momentum Rumbler attacks, if it has first strike (This creature deals combat damage before creatures without first strike.), it gains double strike (This creature deals both first-strike and regular combat damage.) until end of turn.
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