I combined my multi player artifact before I realized what it was. Is there a way to get another? has anyone ever got a 2nd one?

What’s a multiplayer artifact?

If you mean the Multi Level power, then yes, there should by now be two spots, one each on two different maps, that you can collect two times in total when you replay the level later on. If you meant something different, then I don't know what you are talking about.

Based on how you phrase it, I suspect you sacrificed 4 artifacts to upgrade another artifact.

You cant un-upgrade artifacts.

If your question is about the Multi Level power, in total you can pick up 4 of them from playing the normal levels, after that you can buy them for 700 coins or $7 a piece.