Isengard Unleashed only stops damage from being prevented by effects that use the word "prevent" or keyword abilities like protection that prevent damage.

Protection prevents damage, so protection will be unable to prevent damage after Isengard Unleashed has resolved. However, this won't allow a spell or ability to target illegally, even if that spell or ability would cause damage to be dealt.

If a creature with trample you control would deal combat damage to a blocking creature this turn, you must assign its unmodified damage. For example, a 3/3 creature with trample blocked by a 2/2 creature can have 1 damage assigned to the defending player. It will then deal 6 damage to the blocking creature (2 tripled) and 3 to the defending player (1 tripled).

If an effect such as that of Chandra's Pyrohelix asks you to divide damage among targets, you must divide the unmodified damage before tripling it.

If you resolve two copies of Isengard Unleashed in one turn, damage dealt by sources you control will be multiplied by 9. If you resolve three, it will be multiplied by 27, and so on.

"Flashback [cost]" means "You may cast this card from your graveyard by paying [cost] rather than paying its mana cost" and "If the flashback cost was paid, exile this card instead of putting it anywhere else any time it would leave the stack."

You must still follow any timing restrictions and permissions, including those based on the card's type. For instance, you can cast a sorcery using flashback only when you could normally cast a sorcery.

To determine the total cost of a spell, start with the mana cost or alternative cost (such as a flashback cost) you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.

A spell cast using flashback will always be exiled afterward, whether it resolves, is countered, or leaves the stack in some other way.

You can cast a spell using flashback even if it was somehow put into your graveyard without having been cast.

If a card with flashback is put into your graveyard during your turn, you can cast it if it's legal to do so before any other player can take any actions.