252+ Atk Choice Band Water Bubble Araquanid Liquidation vs. 252 HP / 0 Def Druddigon: 165-195 (46 - 54.4%) -- 59% chance to 2HKO
252+ Atk Choice Band Araquanid Leech Life vs. 252 HP / 0 Def Druddigon: 157-186 (43.8 - 51.9%) -- 12.5% chance to 2HKO
Does Water Bubble reduce fire attacks by half? If it does then Araquanid has quite an impressive amount of resistances and should get a decent amount of switch in opportunities.
Power Split is also kind of interesting. Its base offensive stats are so shit that it'll almost always be reducing the power of an attacking pokemon and increasing its own power. If you put max EVs into bulk and go -atk or -spa nature you could REALLY screw up an enemy offensive pokemon. Unlike most other pokemon that have power split it's not really suffering 4MSS because due to the ability, 99% of the time you'll want to use one water attack, even if its resisted.
You could also go for broke with Hydro Vortex.
Ooh, I'm really hyped now! I was already planning on using Araquanid even before the Water Bubble boost was revealed, but now I'm definitely keeping it with me all the way! I did some calcs, and without rain, a fully invested Araquanid can 2HKO a special attacker Magnezone. Of course, this also means it gets 2HKO'd by Magnezone's Thunderbolt, but damn.
I think that might be with Choice Band too though... Still, this squishy spider is definitely looking like a lot of fun!