What do you think? Balanced? Too complex? Is it "grokkable" despite the large amount of text?

It's about as complex as Trading Post, so that's fine. Haggle seems unnecessarily niche as a keyword, however.

It's for a challenge that requires a new keyword.

Is it balanced? Underpowered? Overpowered?

I'm not sure. The only thing I know is that I read the card and immediately went "Ick! Discard 4 cards to draw a card? No thank you!"

I'm well aware that that's kind of an irrational response. I thought it was worth reporting, though, because people do make irrational responses like that.

Do you think it could cost and be fine? It would be strictly better than Jayemdae Tome, but I don't think that's a huge problem for a rare.

This is one of those cards I'd need to play with to figure out how good it really is. There's just too much going on to get a good handle on it.

But as it stands, I think that maybe you should switch the 3 and the 4. It seems to me that the potential for recurring the same artifact over and over again is better than drawing a random card off the top.

Oh, also why does the artifact return say 'up to one'? Why would you ever activate that ability and not target anything?

I think flipping the cost would be too good for the draw ability.

How do I edit this to not let me untap itself with ability 3?

Throwing 'other' in there does make for some awkward wording. Hmm. Maybe it's okay as is?

Maybe "Untap two target artifacts other than ~"? As is, it goes infinite with any combination of two artifacts that can collectively produce 4 mana.

Challenge submission period closed, so too late to change anything now.