Hey there! Voltron is indeed a load of fun (check out my Voltron deck, yes shameless plugs), and I may just have some suggestions for you that I have found in my Voltron journey!

• Aqueous Form , Artful Dodge , Distortion Strike , Invisibility , and Thassa, God of the Sea . I see you already have Aether Tunnel, so if that's been working for you, you might like these too! They work very well for me quite often, especially the re-castable ones.

• Temporal Mastery , it works really well with mystical tutor which you have in the deck.

• Esior, Wardwing Familiar is really good since now any spell costs FIVE cmc, making it really hard to target him.
• Pemmin's Aura : Well it does a lot- it's pretty self-explanatory
• Kaho, Minamo Historian since you run a lot of instants this could be good especially if you use some unblockable spells from above
• Rapid Hybridization / Pongify Cheap blue removal
• Vanishing Lets you phase him out at the end of every turn at instant speed
• Ancient Tomb Great colorless land
• Sapphire Medallion Easy cost reduction

Then again putting kaho and esior will mess up polymorph so

@ DemMeowsephs Thank you for the suggestions! Voltron is a new way of playing for me as well! Yeah, unfortunately adding kaho and eisor would mess up the polymorph plan. Though with Thassa, God of the Sea , Kaho, Minamo Historian , and especially Esior, Wardwing Familiar I think they still have potential as Polymorph/Voltron commanders, with them having a lower converted mana cost and built in evasion, something to look at in the future! The cheap removal cards you recommended were on my radar as well, added them to the maybe board if I find myself needing better interaction!

I agree as well with the recast able unlockable effects! I run Artful Dodge in my Rielle, the Everwise deck! The Crab and our Blightsteel Colossus payoff don't typically need more than one or two attacks to eliminate a player, so it might work! With a primary gameplan to sacrifice the Crab for a polymorph, I'm a little hesitant to include too many enchantment aura effects that make our creatures unblockable, though on the other hand, it could be better in terms of tempo, getting faster crab attacks in the early game. Something to playtest in the future I think!

Tetsuko Umezawa, Fugitive makes the crab unblockable. Then you can use it's activated ability to deal big damage out of nowhere. It messes with the polymorph plan, though...

@ KBK7101 Indeed! Before settling on the crab, I wanted to build a Tetsuko Umezawa, Fugitive commander deck! For sure a cool card! Slightly different flavor of voltron, but I could see it also running well as a polymorph voltron commander!

Unfortunately, with the Polymorph gameplan, I don't really have room for the cooler utility creatures, which is a bit of a drawback. I've been playing this at locals the past couple of months and I've recently even cut Nezahal, Primal Tide just to add even more consistency to big plays!