I've been running Covert Cloak on Max HP Araquanid to dodge the flinch hax.Been soloing with Hisuian Samurott that was suggested by some content creators but might give Araquanid a go solely because shutting down Beads and not having to care for burn rng sounds like a massive plus in exchange for being vulnerable to Dark Pulse flinch hax. Hope you all are having fun with this fish!
I also experimented with 236 Speed EVs to be faster than lvl 75 Chi-Yu. You get the initial Entrainment off before it attacks, so you take less damage from that first move. Getting Skitter Smack and Rain Dance off before Chi-Yu acts has been nice, too. I think Shell Bell is the best item for fast Araquanid in case you're hit by Ruination, since you're not as tanky. I've also tried Ability Shield to always have Water Bubble. Either or works.