I'm not sure if I can make it to the submission because its August 11 in my place already, though I think I'm one day earlier to EST, so...
Arceus-Water @ Splash Plate
Ability: Multitype
EVs: 252 HP / 160 Def / 96 Spe
Timid Nature
IVs: 0 Atk
- Judgment
- Recover
- Defog
- Toxic
Arceus-Water is a hard check to Altarianite Entei thanks to its great bulk and its Water-Typing. In addition, it is also faster than it where it gets a quick recovery option before Entei gets a chance to get a KO and even straight-out OHKO it with a super-effective Judgment. Although, it dislikes getting hit by Toxic unless it runs Refresh or gets burned by Sacred Fire.
252+ Atk Pixilate Entei Extreme Speed vs. 252 HP / 160 Def Arceus-Water: 147-174 (33.1 - 39.1%) -- guaranteed 3HKO after Stealth Rock
252+ Atk Entei Stone Edge vs. 252 HP / 160 Def Arceus-Water: 102-121 (22.9 - 27.2%) -- guaranteed 4HKO after Stealth Rock
0 SpA Splash Plate Arceus-Water Judgment vs. 0 HP / 0 SpD Entei: 384-452 (103.5 - 121.8%) -- guaranteed OHKO