Altaïr Ibn-La'Ahad

First strike
Whenever Altaïr attacks, exile up to one target Assassin creature card from your graveyard with a memory counter on it. Then for each creature card you own in exile with a memory counter on it, create a tapped and attacking token that's a copy of it. Exile those tokens at end of combat.

Assassin's Creed

First strike
Whenever Altaïr Ibn-La'Ahad attacks, exile up to one target Assassin creature card from your graveyard with a memory counter on it. Then for each creature card you own in exile with a memory counter on it, create a tapped and attacking token that's a copy of it. Exile those tokens at end of combat.

Although the tokens enter the battlefield attacking, they were never declared as attacking creatures. Abilities that trigger whenever a creature attacks won't trigger when they enter the battlefield attacking.

Each of the tokens copies exactly what was printed on the card in exile and nothing else. They don't copy any information about the object the card was before it was exiled. 

If a card copied by one of the tokens had any "when [this permanent] enters the battlefield" abilities, then the token also has those abilities and will trigger them when it's created. Similarly, any "as [this permanent] enters the battlefield" or "[this permanent] enters the battlefield with" abilities that any of the tokens have copied will also work.

If an exiled card has {X} in its mana cost, X is 0.

You choose which player, planeswalker, or battle the tokens are attacking. Each token can enter attacking a different player, planeswalker, or battle, and they don't need to be the same one that Altaïr is attacking.

Copy

(This token can be used to represent a token that's a copy of a permanent.)