Here we have Sol, the Luminary of the sun. As noted by his flavor text, he trained both Mars and Mercurius, so his Red/Blue typing makes sense. With only 5 colors in the game, I had been wondering how they were going to churn out Seven different Luminaries, but dual-typing some of them is a nice touch. Sol's ruler side is pretty cut and paste from his two disciples: RU1 Judgment, energize (but with the two-color option), and the Mana keyword, which he can use for either blue or red. That alone makes him objectively better than Mars and Mercurius in pretty much every way, being able to play any Ancient Magic they could all by himself.
Flipping him, though, is where the differences start to show. He has the standard Mana 5, and gets 5 more if you remove his respective demon familiar when flipping him, but he only comes in with a measly 500/500 body. By removing his minion from the game, he gets a hefty 600/600 stat buff and enters as an 1100/1100 (It's also worth noting that this is NOT an automatic ability, it simply happens as he enters, so you can't chase something like Space Time to his entering the field to cheese him). That puts him 100 ATK and DEF over his students, but without a keyword. Mercurius' Flying is an extremely powerful bonus, so it might make you stop and think about which Ruler to run, but I respect that FoW included that opportunity cost. This guy being able to use all of Mercurius' Ancient Magics, PLUS Mars', is way too strong to not hamper him just a little. Coming in as a 5/5 if you're forced to flip without having his demon in hand is a nice catch to him in my opinion. It at least keeps him from 100% power creeping the previous two out.
Speaking of his familiar, let's look at how it stacks up to Mars' and Mercurius' little buddies. Runic Commander Demon, Akiot (try saying that 3 times fast) has the standard 600/600 body for a 2-drop, putting him at 100 ATK/DEF above the other two familiars, just like his master. Continuing the parallel, though, he's lacking in keywords like Namblot and Astaroth. On enter, he puts a mana counter on your J/ruler, and you can bounce him whenever you play a chant. To me, this feels a little lackluster, although I suppose it needs to be. Namblot automatically bounces himself at the end of the turn, but is packing swiftness and has the potential to kill something with his burn effect. That gives him decent aggro/removal power while simultaneously protecting himself. Astaroth draws a card on-enter, netting you hard advantage, but requires you to pay 2 water to bounce him. Akiot has no way of giving you advantage, and there are plenty of easier and cheaper ways to give your J/Ruler a mana counter that don't risk your familiar dying and you losing out on 5 counters later on. But, as I said, Sol needs a bit of a handicap so he doesn't completely outshine the other two.
Twin-Headed Dragon is an interesting card. Being Blue/Red, he fits right in to Sol's deck, but can just as easily be tossed into Mars or Mercurius. A 1000/1000 flier for 4 mana isn't the greatest thing in the game, but it isn't the worst either. Being able to pay his awakenings with mana counters is an awesome mechanic too, and I kind of wish you could pay his whole summon cost with Mana, but that might be a bit too much. Awakening with red will burn a resonator for 1000 when he enters, and awakening for blue will rest two resonators and keep them like that for another turn. Mercurius and Mars can each make use of one of his Awakenings with their Mana, but only Sol can get the most efficient use out of both of them. This guy is a HUGE tempo swing, capable of removing up to 3 of the opponent's big players from the equation, at least temporarily. He's also a great way to bait out negation/counter cards that would otherwise be used on your Ancient Magics.
Speaking of Ancient Magics, here are the two that got spoiled for us today. Conjure Time Bomb, for the low cost of 2, will create a 100/100 "Fire Bomb" resonator token that, at the beginning of your next turn, will blow up and deal 1000 damage to your opponent AND all J/resonators they control. If you awaken it for RR1 more, the timer is shortened drastically and it explodes at the end of your turn, so if your opponent isn't packing immediate removal, they're gonna have a bad time. The amount of tempo this card can earn you is MASSIVE, especially against decks like Fiethsing Turbo or Fairies, that like to go wide and flood the board.
The other beauty is Rune of Sol. For RU, you can grab ANY Ancient Magic from your deck and add it to your hand. With QUICKCAST. What. Got some unused will before untap? Why not search for your big finisher card. The fact that this can be played with Mana counters is just insane. Sol can now run 1-of's of any Ancient Magic and not sweat seeing them. Mercurius just got 4 more consistency cards to ensure that big Rising play is going to happen. Mars can nab Invitation to let you know you're about to die. Black Moonbeam is searchable.
Rounding out today's spoilers, as usual, is the new Special Magic Stone. Magic Stone of Vaporization has the standard Shockrock text of coming in tapped if your J/ruler isn't Sol or you don't pay 300 life, counts as both the Fire and Water Magic Stones, and can produce both colors. It's unique effect is, by tapping itself and any other will source, you can put 1 mana counter on your J/ruler. You have leftover stones before you're about to recover? Turn them into permanent mana counters. That's just absolutely insane.