Scavenge

[Gorzo]

I've been told that I can't use it to scavenge anything I want because scavenge says you have to exile that exact card

You do have to use scavenge on the card card with scavenge. So for example if you have a {deadbridge Goliath} in your graveyard, you may pay its scavenge cost to use its ability and exile it to add 5 counters to a creature.

As for copying it, Rule 706.10 states you can copy fling, I don't see why you wouldn't be able to copy scavenge along the same line.

[Malleo]

And it just occurred to me that a copied scavenge might work like a copied fireball

[Malleo]

Just checked the rules and my original plan holds