If, during your declare attackers step, Frontline Rebel is tapped or is affected by a spell or ability that says it can’t attack, then it doesn’t attack. If there’s a cost associated with having it attack, you aren’t forced to pay that cost, so it doesn’t have to attack in that case either.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.