For the first run of the cube 360, I will not have the following cards in the cube with reasoning in paratheses:

• Stoneforge Mystic (not a knight, not really on theme of cube, could return)
• Dragon Wings (in general bad targets in colors, not likely to return)
• Day of the Dragons (very niche, but could be cool in some builds, may return)
• Feed the Swarm (too painful in most cases, not likely to return)
• Slumbering Dragon (will probably never be online before it can do anything. not likely to return)
• Hoarding Dragon (Not many good artifacts to get, not likely to return.)
• Ryusei, the Falling Star (doesn't kill much on death, feels bad, not likely to return)
• Sarkhan, the Dragonspeaker (kinda underwhelming maybe? Needed cuts and seemed like a candidate, could return)
• Form of the Dragon (was added for theme of cube, is ultimately really bad lol, not likely to return)
• Whirlwind (I think I added too many "boardwipe flyers" cards, and the others have more uses, may return, but not likely)
• Boxing Ring (I need to add more fight cards to the cube for this to be better, not likely to return)
• Atarka, World Render (needed cuts, gruul was a little big, could return)
• Karrthus, Tyrant of Jund (may be too heavy in deciding games, could be cool though, may or may not return)
• Sol Ring (xd I just wanted a sol ring, will not return)
• Chromatic Orrery (high cost might not make it worth, but with some tweaks it could, may return)
• 3x Haven of the Spirit Dragon (I would like to find more cuts to add more of these to cube potentially, probably will return)

The following cards are on watch for being replaced:

• Baneslayer Angel (may be too much of a stonewall)
• Sword of Fire and Ice (may replace for a non-red sword if too strong)
• Ugin's Nexus (may be too niche since no extra turn spells are in it, but the copy permanent spells make it cool)
• Dragonstorm (storm might not be that good, or if the storm is there, then this might be insane, will weigh it in the group)
• Reason // Believe (might just suck!)
• Teneb, the Harvester (colors are too niche maybe, might never do the thing)
• Inferno of the Star Mounts (might just be a flyer haste 6/6 with firebreathing most of the time)
• Empty the Warrens (storm issue if it's there or not, niche uses)
• Glorybringer (can't target dragons so it might suck lol)
• Voracious Dragon (goblin generation may not be enough)

Might make more changes on the fly, but that's where I'm starting.

Cards I am considering adding in the future:

• Purphoros, Bronze-Blooded (I want an effect of this kind in the cube)
• The Ur-Dragon (probably way too over the top, but idk)
• Clever Impersonator (Thought it was in there already, will need to add it to the cube)
• Chromium, the Mutable (was in the cube earlier on, probably a good card for a WUB build)
• Recurring Nightmare (sac outlet and recursion, might be too strong with some cards though)
• Swan Song (soft counter that makes a potential blocker)
• An Offer you can't refuse (another soft counter that could fuel opponent gameplan)
• Arcane Denial (probably healthier than straight counterspell)
• Magda, brazen outlaw (get dragons for your treasures!)
• knight exemplar (I forgor)