Returned Pastcaller (U)
(yes)
Creature -- Spirit Cleric
4/2
Flying
When Returned Pastcaller enters the battlefield, return target Spirit, instant or sorcery card from your graveyard to your hand.

I just posted this card so I could say UGHHHH.

That name is... kind of tragic. The mana cost actually amuses me, though I'm not sure how different a balance it is from . If it had a CMC of 3 or 4 that hybrid symbol might matter to a tricolor deck or one running unfortunate numbers of non-color-producing utility lands, but out of 6 sources I don't think you ever really muster CD but not H.

This looks... Not very good.

Eww, gross. There is simply no reason for that mana cost.

Half generic, half colored, colors running one into the next, oh yeah. Little high for the effect though.

If you get two, that's a loop of unkillable 4/2 flyers in Limited. Six mana makes sense to me.

Not a bad point. It's a reliable finisher that way, but it's not fast so you'd need to control the board for a while before you win. Still worth drafting if you think you can snag 2.

Eternal Witness is considered above the curve. This is consistent with Archaeomancer and Izzet Chronarch. Higher mana cost isn’t so bad as you’re more likely to have a target by then

I'm not a fan of the mana cost, er, MANA VALUE, BTW. Much rather it was or

...except what you described IS mana cost. Mana Value is the new term for CMC.

Including this cycle in stx is a low risk way of seeing what players think of these sort of mana costs before they decide whether to use them more in future. And maybe there's a card that's too good at but too weak at

feels like a bankai mastery design

It's been a long time so maybe I am remembering it wrong but I think back in Return to Ravnica (2012) they said that there were more 5 color decks in limited than they wanted. Given the fixing and the power of the gold cards it was worth playing them even if both colors were splashes. The next time they went back we had the Crackling Drake cycle to encourage people to stick to 2 colors but with that you will sometimes just not draw the right lands. I think this is the next step in trying to make cards for 2 to 3 color decks in sets with lots of gold cards.