Going
deep on this one. I already have a "historic/legendary matters" subtheme and I loved the
Kethis, the Hidden Hand combo deck in Standard, so I'm trying out adding a few cards to get most of that deck into the cube: we've got
Mox Amber,
Rona, Herald of Invasion,
Tyvar, Jubilant Brawler,
Honest Rutstein, the whole nine yards.
What's the pick:

The former works with Tyvar and more easily becomes Kethis or Rona. It's better in the actual combo deck, but you (generally) would be embarrassed to play it in other decks - though I do have
Abhorrent Oculus /
Helping Hand /
Sevinne's Reclamation so it's certainly not impossible.
The latter requires a crime, but you can also just turn it into a
Griselbrand or whatever, and I do have Reanimator as well. So a bit of cross-theme synergy.
...alternatively, do I just say screw it and play
Baleful Strix because nobody in the history of Magic has ever been sad to cast that one? I think that's not right, but I never know how deep is too deep.
Current list is at
https://cubecobra.com/cube/list/seekerscube.