Calyrex-Shadow is emblematic of a lot of the problems with Pokémon’s core game design. The structure of battle is by nature biased towards offensive threats that can make progress against the opponent as opposed to defensive play that is actively discouraged and cannot keep up with offensive power creep. Even the strongest and most controversial stall teams can be broken through with cores consisting of broken offensive threats like these whereas it is much, much harder for the other way around to happen.I despise Calyrex Shadow Rider with every bone in my body. I don't think its particularly interesting design wise, but I hate the way its designed gameplay wise.
It has the offensive stats of a glass cannon, but not terrible defensive ones. The only thing holding it back defensively is its typing, which can be solved by tera. It just feels so braindead to fight with and against because it's just lets out speed and ohko both pokemon with my 165 spatk 120 bp spread move that has no downsides.
I just don't like what it represents balance wise, I think ice rider is better designed because it has a bigger drawback that can't just be solved by tera, its low speed. But that can also be played around with strategically with trick room. I think it requires more thought put into playing it, and is a lot more interesting and fun to fight against.
Speed has always been a hilariously overturned stat in these games and I think it’s that Ghost typing, Astral Barrage paired with As One and specifically that base 150 Speed that makes Calyrex-Shadow so dominant. Similar to Dragon-Types, being a fast Ghost-Type means you can threaten opposing Ghosts which can lead to decreased parity between the amount of viable Pokémon in the metagame. Calyrex-Shadow is the fastest Ghost-Type in the game and gets the jump on even Zacian-Crowned’s base 148 and almost all other manner of restricted Legendaries and stuff like Paradox Pokémon, and it can still hold an item unlike Zacian-Crowned. That Speed and Ghost’s lack of resistances outside of Dark are what allow Astral Barrage spam to spiral out of control too quickly. What this also means is that you have to play the mental guessing game of what item the opposing Calyrex-Shadow has if you’re also running one, since if it’s Scarfed and yours isn’t, you can’t try and reliably use it as an offensive check to the rest of your opponent’s team. And if both of you are Scarfed and/or if you’re an Imposter Ditto against one that is also holding Choice Scarf, it goes back to being a Speed tie anyway. There’s a reason Gen 8 Ubers runs through this and the Big 3 and it’s banned outright in Gen 9.
The idea of Calyrex-Shadow not looking as overpowered as you might think it is reminds me a lot of Zacian-Crowned and the Paldea mascots relative to a Mega Rayquaza or something like that. Koraidon and Miraidon bother me for a few reasons but that high Speed and strong typing is something they all have in common, leaving little to no room for anything else to surpass them in viability. Should Primal Groudon make a return that could help with and against those two, but it’s also going to be just another Astral Barrage magnet, since I don’t see Primal Kyogre or the Dark-threatening Xerneas (for Calyrex teams) being good if they make it to Champions. All of this while ignoring Mega Rayquaza, who probably won’t be able to use Max Airstream to help in the Speed-centric effort to get rid of Calyrex-Shadow early and often.
And I STILL haven’t mentioned that Calyrex-Ice is weak to Ghost just to make things even worse around this thing. This and Lunala are both popular in modern Trick Room teams in VGC and Calyrex-Shadow requires those teams to play on the back foot until they’re absolutely certain they can set up.