Ika, could you comment on the increasing trend of Char-X fini steel mon cores? What is particularly curious to me is that these Zards are running wisp, which is an inherent non-bo with its common partner, fini. What is the strategy behind it?
Regardless, thanks for the team dump, definitely a ton of gems here! Ika our lord and savior of BSS!
Rather than me explaining my personal opinion solely although it is pretty similar to what I will write below, I'll try my best to reiterate what is written in blogs about specifically Charizard X + Tapu Fini as a general pairing duo. It should be noted that there is generally a steel type in every top team due to the defensive utility of steels as Tapu Lele, Mimikyu and to a lesser extent Naganadel and Mega Salamence checks so I'll try my best to explain that later.
Whilst it is true that the abilities of Tapu Fini and Charizard X do not really mix very well, the typings themselves are very synergistic and both pokemon are naturally, especially with the bulkier EV spreads very fat and therefore able to cover each others weaknesses. Charizard X smacks grass/electric types that typically give Fini trouble (like Tapu Koko, Ferrothorn, Breloom and to a lesser extent Thundurus-T) whilst Fini deals with the Ground, rock and dragon type attacks that give Charizard trouble due to its natural bulk such as Hippowdon, Garchomp and Landorus-T. One thing in particular important in the Charizard matchup is getting rocks up, however most of the major setters (Lando, Hippo, Garchomp and Heatran) struggle heavily vs. Fini whilst Ferrothorn can be switched into and taken advantage of for free by Charizard X. In this way, setting up SR can be difficult before Zard X is already megaed, at which point SR is not as important.
Will-o-Wisp on Charizard X obviously is blocked by the Misty Terrain, but this does not occur in all cases, for example switching in Landorus-T into Zard X to apply intimidate or to threaten out with EQ, which can still be wisped. The other major case is Mega Gyarados, which prefers not to mega due to Tapu Fini existing. The second thing is, that in these sorts of compositions, it can be common to lead Zard in certain matchups and get off early wisps, for example if the opponent wants to lead Mimikyu. Bulky Zard spreads can surprisingly handle, given the right EV spreads, a lot of the typical non-ground leads such as Tapu Koko and Sash Greninja. Will-o-wisp is also very free vs. Hippowdon compositions since they have no switchin to Zard Y (if they get the mindgame wrong) other than typically Mega Salamence which hates Wisp and Zard X can roost stall Hippo EQs after a wisp relatively easily whilst Misty terrain blocks yawn.
To put it a different way, rather than using Zard X's natural strength with tough claws (though bulkier spreads use this anyways), the composition uses Zard-X's bulk and defensive typing to chip down opponents in what would probably tend towards balance rather than offence. This sort of composition also benefits off multiple mindgames, is it Zard X or Zard Y and then when you have found that out, is it SD Zard X or a bulkier variant which can make it difficult for opponents to form cohesive gameplans.
A steel type just completes the Fairy Dragon Steel core. Celesteela is generally preferred due to its ability to leech seed, punishing switches as well as its ground immunity which further neuters the likes of Scarf Landorus-T which could otherwise wreck havoc on the core.
