No, it doesn't - its effect REQUIRES it to attack all your opponent's monsters. You don't have a choice in the matter. So that means if it attacks a monster with higher ATK, then Ultimate Tyranno is destroyed. You may want to choose to attack that one last, and get rid of your opponent's weaker monsters first.
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"its effect allows it to attack all monsters"
No, it doesn't - its effect REQUIRES it to attack all your opponent's monsters. You don't have a choice in the matter. So that means if it attacks a monster with higher ATK, then Ultimate Tyranno is destroyed. You may want to choose to attack that one last, and get rid of your opponent's weaker monsters first.
then it's destroyed, same as any other attacking monster with an atk lower than its target