It only creates an additional combat and main phase if it resolves during a main phase.
If you manage to cast this during a main phase of your opponentâ€™s turn, that opponentâ€™s creatures will untap and that opponent will be able to attack again. It will not allow you to attack during their turn.
Abilities that trigger when a creature attacks, blocks, or is blocked will trigger during each combat that turn. Thus, a creature with Rampage will get the bonus added during each attack.
A creature that must attack each turn, must only attack once that turn. It is not forced into each attack that turn.
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