If a card in your graveyard has in its mana cost, X is considered to be 0.

Any effects that applied to Likeness Looter before it becomes a copy of another card will continue to apply after it becomes a copy. The same is true of any counters that are on Likeness Looter.

If the copied card has an ability that can be activated only once each turn, copying that card a second time will allow you to activate the new instance of that ability.

Because Likeness Looter isn't entering the battlefield when it becomes a copy of a card, any "When [this creature] enters the battlefield" or "[This creature] enters the battlefield with" abilities of the copied card won't apply.

Likeness Looter copies exactly what was printed on the original card and nothing else, except the characteristics it specifically modifies. It doesn't copy any information about the object the card was before it was put into your graveyard.