You could just call this the big red flag on the field. S0 is a Rank nothing (but always treated as 1) Light Warrior-type XYZ Monster with ? Atk and ? Def. It gains 1000 Atk and 1000 Def for each XYZ Material attached to it. It requires 3 same Rank Number XYZ Monsters to XYZ Summon this card. So we're looking at 3000 Atk and 3000 Def when this thing hits the field properly. What happens to the original monsters' XYZ material? Anyway, the alternate XYZ Summon method is by far easier. Just control a Utopia monster and discard a Normal Spell Card with Rank-Up Magic in the name. So if you don't have a RUM Spell, go lightning, and if you do go for S0. It's great to have options. Either method for XYZ Summon is immune to negation, and your opponent cannot activate anything. 
So after all that, what do you get? An on-destruction effect? nope? Protection from tributing Kaijus? Don't we wish. A board wiping effect? Not even. S0 can detach a material during the opponent's turn to prevent ALL card and effect activations for that whole turn. Imagine drawing Heat Wave after this. GG no re. Abuse it. Warning: may cause rage quits. 
 
Score: 4.5/5
Art: 5/5
 
-WarlockBlitz

Number S0: Utopia ZEXAL
 
Today's COTD is Number S0: Utopia ZEXAL, a Protagonist's Ace monster that should have been good but trips and falls flat on its face at the finish line. S0 is supposed to represent the final evolution of Number 39 into an unstoppable force, but unfortunately it doesn't.
 
S0 has no rank of its own, but a condition on the card says it's always rank 1. S0 has a base attack and defence of 0 on a light warrior Xyz body. It can either summon itself by using THREE Number Xyz monsters with the same rank, or you can discard a Rank-Up-Spell card and overlay S0 over a Utopia monster you control. Now, by giving up three Number Xyz monsters, you're losing a lot of field presence and potentially losing a lot of advantage. The chaos-overlay is actually the better summoning option of the two, given you only need to use a spell and any utopia monster, which is easy enough to do with R4NK decks.
 
Now, when you DO sumon S0, his summon can't be negated and the opponent can't respond to his summon. Both good effects, and this is where he stumbles. S0 gains 1000 attack and defence for each material on him, so you've either got a 3000 monster after losing advantage, or a 1000 to 4000 monster after ranking another Utopia monster into it.
 
Lastly, and this is the part of this monster that drags everything else down. Once per turn, during the opponents turn ONLY, by detaching a material, the opponent can't activate any effects until the end of the turn. He has no protection, doesn't stop continuous effects, he can't stop whatever he's chained to and he doesn't prevent anything being chained to him. That, coupled with only being able to use this effect during the opponents turn kills it.
 
He looks pretty neat though, right? And he certainly fits right into a Yuma fan-deck. But with extra deck space getting tighter with each new set, and better Utopia monsters out there, looking at you Lightning, S0 is mostly an un-used card.
 
Advanced 3/5

Number S0: Utopic ZEXAL:
 
After looking at the Code of the Duelist preview cards, we can now look at the cards that were reprinted just so Europe can now access them. First off of the two is the one that is clearly better, and that is Number S0: Utopic ZEXAL.
 
S0 is one of the few monsters with no stars as a monster along with Tzolkin, Bishbalkin, F0 (both versions, one of which is currently OCG exclusive), and every Link monster currently printed and likely will be printed. ZEXAL can be XYZ summoned using 3 Number monsters with the same Rank. Spoiler Alert: that isn't happening unless the stars align. S0 is always treated as a Rank 1, which doesn't matter. Now we can see how this card is summoned. ZEXAL can be XYZ summoned by discarding a Rank-Up Magic and using a Utopia monster as material, along with that Utopia's XYZ materials. This is a way more realistic way to summon this guy, the only negative is that you have to run Rank-Up Magic cards, which can suck, but if you want to be cheeky and run Seventh One, then have at it, cause top decking that card can be fun. The XYZ summon of S0 cannot be negated. That sounds very promising. S0 gains 1000 ATK for each material it has, which means it will likely be at 3000 or 4000 ATK and DEF unless you want to run as many Utopias as possible to put on top of each other. Finally, on your opponents turn, you can detach a material to stop your opponent from activating cards or effects during that turn. This is why this card is so good, not letting your opponent play Yu-Gi-Oh on their turn is so crucial, and it could easily lead you to OTKing them. It doesn't stop them from dropping Kaijus, which are really their only hope, but this card just helps you end your opponent if you couldn't already.
 
This card is very good, and makes up for having to run Rank-Up Magic cards, as Brilliant Fusion makes up for you having to run Gem-Knights.
 
Advanced Rating: 4.25/5