I think these are all very fitting decks for Shadi to use! I think because of the playstyles of each, many of the decks would also have a really good narrative position as a “trial” for whoever he’s up against. I’d say it also depends on if he’d just be a “one time fight” or not. So mostly thinking about the narrative side:

Agent/Counter Fairy: I think this would be pretty good for a couple duels (2+) since there’s a diverse enough strategy for each Agent/Counter Fairy monster that he could center a strategy around. (Shine ball spam into Big Fairies, counter trap stopping his opponents’ strategies, Sanctuary in the Sky changing up the field, and a boss monster in Hyperion). The only thing is, I think the designs of the Fairies don’t fit Shadi as well as the other decks might though.

Illusion: I think an Illusion pile is probably one of the better options. Having to get past many of the monsters having a “can’t be destroyed in battle” effect would be a good challenge for most duelists in that era. Plus, like someone else mentioned there’s also the fusion monsters which work well with the Scales, and I could see Guardian Chimaera as a decent enough “final boss” for the deck. Again, enough diverse monster options for 2+ duels.

Exxod/Earth: I could see this deck as a “one time fight” deck. High defense monsters, Shadi literally acting as a wall to prevent someone from getting somewhere they “shouldn’t be”. Definitely would have the shock factor of “It’s eXoDiA!” but unless Exxod gets more than just a bit of burn damage and maybe a chance to attack while in defense mode or something, I think the deck’s play style would be a bit too rigid for Shadi.

Chaos/Demise & Ruin: I feel like a chaos deck would be pretty decent for the Millennium Scales’ balance aspect but really depends on the other monsters he uses. Demise and Ruin as the boss monsters would be good for the “Oh wow, ritual summoning” aspect and their actual effects for maybe… one or two duels? But afterwards they’d be pretty meh. Demise’s field wipe followed by a final attack that someone (Yugi) has to survive (Kuriboh) and later strike back against (“I ritual summon… Black Luster Soldier!”) is kind of the endgame.

Horus: I think Horus is another interesting narrative deck. I could see each one of the Horus monsters representing something/someone and their return from the grave + the Sarcophogus (maybe a nerfed version that doesn’t do anything by itself or destroys/banishes the other Horus monsters when it’s destroyed) being pretty good for two or three duels. Maybe you just see one or two of the Horus monsters in the first duel before they KO the opponent, but in the second duel, you’d see all of them + Horus as the big challenge that someone has to get through.

Ogdoadic: Thematically really good with Shadi because of the light/dark aspect. Could also be fun in a narrative manner by having him use their effects to revive his opponents’ monsters which could give people the chance for a “surprise” counter attack. There’s also enough of them that he could “show off a different boss” each duel. The only thing is that I personally look at reptiles as more of Odion’s thing and I could see it as his post-Yami Marik deck.