Oh please Rusey, don't bring in the whole evil guy bias thing into this, that garbage was just something Bocchi made up to try drive his own goals forward.
All in all there's a rather simple answer to this.
While its an item, its easier to count as a 'beast' because A, organizing reasons, and B, I have a nagging suspicion if its made into an item yet 'challengeable' somebody is sooner or later gonna try use that as an excuse to turn every claimed item/anything into 'challengeable', so its better not to go there at all.
Plus well, its mainly just the same few 'competitive' people that mess with the beasts that have any interest in the thing besides me anyway, so there's no harm letting them brawl over it like rest of the beasts.
Further still, you don't even have to consider me into this IC-wise either, assuming if anyone ever gets to even mention the thing outside of forum without being bogged down by challenges. I never acknowledged having lost the thing to Bocchi in the first place, so you gaiz can do whatever you want with the 'official' mazo, I'm still gonna keep mine >>
And just so you all can be particularly lazy about it if you desire, I'll even make it even easier. If any of you competitives do feel the need to absolutely make up a reason the mazos out and about ownerless, you can just pretend after Kyu disappeared his stuff went to me, except the mazo which somehow got free and went to go about its business on its own, or was commandeered by rogue zetsus or whatever, iunno.
That way nobody has to try character control or claim stuff about anyone, I keep my stuff and mazo, and you guys get your own mazo, and everybodys happy. Well, unless whoever gets it plans to RP with me about it later on, tho I suppose that'll be an issue for me and said person to deal with whenever if ever such an occasion should arise.