It is pretty good.
Despite facing competition from the bulkier Cresselia, Mimikyu's Disguise allows it to guarantee Trick Room. While it's true most Pokemon sets here use Speed EVs and +Spe natures, there are several great Trick Room abusers you can consider. The first Pokemon that comes to mind are usually Weakness Policy Glastrier (I assume you're going to be playing Battle Stadium Singles with this Mimikyu), Quiet Heatran with Eruption, Belly Drum/Curse Snorlax, Amoonguss/Tapu Fini, Incineroar, even Landorus-Therian. However, with Series 8 being unrestricted, you get several more options, such as Weakness Policy Calyrex Ice Rider, Weakness Policy Necrozma Dusk Mane, Zygarde, Magearna, even Kyogre with Water Spout.
If you want to build a Trick Room team, you might want to consider those Pokemon. However, remember you can only use 1 restricted Pokemon. You should choose whatever fits your team best. I'd recommend having a backup Trick Room setter like Cresselia, and maybe a Pokemon that can function well in and out of Trick Room.
Bottle Capping your Mimikyu is definitely a viable option too, though
Mimikyu is known not just for its ability to set Trick Room easily, but for its ability to revenge-kill many dangerous threats that can quickly destroy a team. Disguise will let it set up a Swords Dance for free. If the enemy outspeeds or if you suspect they have Choice Scarf/are going for a priority move such as Bullet Punch, use STAB Shadow Sneak to pick them off. Mimikyu is infamous for being able to threaten boosters like Blaziken, Dynamax Zapdos, Naganadel, Calyrex-Ice, and Calyrex-Shadow