I remember when my friend was playing Nekroz and he would summon Number 52: Diamond Crab King in Atk position. He would also forget that he had Unicore on the field and would attack something of mine after detaching a material. I would laugh and put his monster in the grave and he'd be like 'wtf?! 3000 atk!' and I would point to his Unicore negating the XYZ monster. And we would laugh. 

Anyway, Diamond Crab King is a Rank 4 Earth Rock-type XYZ monster with 0 Atk and 3000 Def. Like many of the number XYZ monsters, this card is considered a part of the Rank 4 toolbox. Any deck with Level 4 monsters can summon this with any 2 of those monsters on the field. By stats alone this is just a 3000 Def wall.
 
By effects, Diamond Crab King can detach a material once per turn to make its Def 0 and its Atk 3000 during that turn. Then if it attacks it goes to Def position at the end of the Battle Phase. This effect allows it to have a huge Atk stat when it needs it, and a huge Def stat during your opponent's turn. The drawback effect is that if it has no XYZ material it stays in Atk position with that 0 Atk. So basically you attack with it twice and then try to get it off the field. Finally, you can only control one Diamond Crab King. I don't even think the one needs to be on the field. 
 
Score: 2.5/5 Many Rank 4 monsters are better. It's just begging to be Veilered.
Art: 4/5 I get it. And I like it. 
 
-WarlockBlitz

Number 52: Diamond King Crab is the definition of a mild upgrade over last-gen extra deck filler. It’s a 3000 ATK beatstick for rank 4’s that replaced Gem-Knight Pearl as the best option for that unwanted business. And that’s not mentioning the fact that this monster becomes a major liability if its effect gets negated. XYZ and Synchro monsters are well-established in today’s game with a wide variety of tools, which means if you can’t fill up 15 slots with meaningful cards, you’re probably not thinking about it hard enough (or you’re running monarchs).
 
Now, when I look at new cards, I always try to look at it from the perspective of future potential, including watching what’s coming out in Japan or just keeping in mind the potential that exists. Could a card that’s not so good right now be abused in the future should support be released? A perfect example would be Pot of the Forbidden which came out in Dimensions of Chaos. As of today, it’s not a card used very often. However, the effect in itself is outrageous, and due to the presence of Prediction Princess and the future release of excellent cards like Spirit of the Autumn Breeze and Pre-preparation of Rites, I know it’s about to become very good. And that’s only considering what I know is coming. But if I also consider what could come one day, I would rate the future potential of Pot of the Forbidden very high, because I know one day it’s going to be banned once something comes along that easily abuses it.
 
Unfortunately, Number 52: Diamond King Crab does not have that potential. Unless new rock support comes along that utilizes its effects well, I can’t see any future potential in this card. It will probably always be just a beater unless it gets specific support, which it won’t.
 
Advanced: 1/5
Future Potential: 1/5

So today the card is Number 52: Diamond Crab King. So while it has Xyz materials equipped to it you can make his 3000 DEF become his ATK until the end of the turn. Hmm.. pretty solid. 3k swings over all the monarchs, goes head to head with Kozmo Dark Destroyers, and almost all things PePe can throw at you. Along with this he changes back to DEF position after attacking which gives him safety for next turn. And only needing 2 level 4 monsters it's very easy to bring out. Tellarknights, PePe, and any assortment of decks that can use 2 level 4 monsters can make this. The only downside to this is that if it doesn't have any Xyz materials it's changed into ATK position and then it's a zero ATK monster getting swung into. So while it may have very good ATK and DEF situationally and can be summoned very easily along with the fact that level 4 engines are generally the best in the game. \
 
Rating: 3.5/5 
Art: 3/5 (needs more butter)