With Entei now being in Gen 8 NU, there's this set that has been passed around apparently. It's called VinTei. So, here it is:
Gen 8 NU
Entei @ Leftovers
EVs: 132 HP / 252 Def / 100 SpD / 24 Spe
IVs: 0 Atk
- Calm Mind
- Lava Plume
252 Defense EVs is to help with Entei taking physical attacks. 24 Speed EVs allow you to outspeed max speed Adamant Tyrantrum. 100 Special Defense EVs allow you to take some special attacks. The rest of the EVs go to HP. The ability Pressure is so you can pretty much PP stall a Pokemon.
Substitute allows you to scout Pokemon attacks, protect yourself from status, and to set up Calm Mind. Calm Mind boosts your special attack and special defense. Protect is to allow you to get a free turn of Leftovers recovery, and works well with the ability Pressure. Lava Plume is STAB that has a 30% chance to burn, meaning it can cripple physical sweepers and wallbreakers.
Entei appreciates a Pokemon that can deal with rock types. Flygon can do that, as it resists rock type moves. Flygon's ability Levitate also helps with Entei's ground weakness. Flygon can also serve as a Defogger to help clear Stealth Rock which helps out Entei. Vaporean can easily switch into water type moves, allowing it to absorb water moves with its ability Water Absorb. Vaporeon can also provide Heal Bell support that helps out Entei should it be statused. It can also wish pass to help Entei stay healthy.