I would not play Mutilate. You can cast Drown in Sorrow or Dakmor Plague off signets and duals... there just isn't reliably a ten-swamp deck that actually wants a sweeper.
Reborn Hero is vastly too small to do anything, recurring a 2/2 for 3 -- once you achieve threshold -- for double white mana just doesn't provide enough value.
Unifying Theory is somehow vastly worse, it's ten mana and five spells cast to become Tidings AND it lets your opponent keep up.
Sunblast Angel does just seem insanely good. The Boros angel was discussed recently (in this thread? somewhere) and it's definitely not GREAT but it sure is complicated.
Doppelganger seems fairly bad... it can almost never block, is a horrible top-deck, and doesn't even work well with blue's best creatures (Mulldrifter and Whirler Rogue). There's at least some potential for a Pelakka Wurm deck I guess, but on average I definitely don't want it in my Cube decks.
Bazaar Trader.... uh, no. This isn't Zedruu EDH.
Goliath Sphinx has potential -- but it's seven mana for a basically-vanilla creature. Still, it's freaking enormous.
Dawnbringer Charioteers is just Seraph of Dawn 95% of the time, and if you DO have a Heroic theme it's probably way too good to be anything other than rare.
Cursed Scroll wouldn't be super-crazy in C/Ube (closer to Grafted Wargear than to Skullclamp as far as busted colorless cards) , but for it to become uncommon means it has to show up in an actual draftable set which is absolutely never going to happen... it can't show up in any paper set because it's on the Reserved List, and it became a MYTHIC in MTGO-only Tempest Remastered.
Though TBH we're probably more likely to get an upshift to Crystal Shard. But who knows.
Do you need a fifth, worse version after
But it's a definite upgrade to the likes of Sulfurous Blast and probably Breath of Darigaaz.
Unifying Theory is somehow vastly worse, it's ten mana and five spells cast to become Tidings AND it lets your opponent keep up.
Sunblast Angel does just seem insanely good. The Boros angel was discussed recently (in this thread? somewhere) and it's definitely not GREAT but it sure is complicated.
Bazaar Trader.... uh, no. This isn't Zedruu EDH.
Goliath Sphinx has potential -- but it's seven mana for a basically-vanilla creature. Still, it's freaking enormous.
Dawnbringer Charioteers is just Seraph of Dawn 95% of the time, and if you DO have a Heroic theme it's probably way too good to be anything other than rare.