Azumarill @ Choice Band
Ability: Huge Power
EVs: 172 HP / 252 Atk / 84 Spe
Adamant Nature
- Play Rough
- Waterfall
- Aqua Jet
- Superpower
Entei tends to burn switch ins like Rotom-W and Slowbro. You can include less common things like Alomomola here too. Although Azu already does a number to them with Play Rough, they will have to think twice before switching in on Azu when burned. The chip damage from burn + SR will leave them significantly more weakened than they normally would be after switching in. Other water types like Quag take heavy damage from Play Rough and don't appreciate burns from Sacred Fire. This all shows how Entei and Azu can overload many of the bulky waters they are checked by. Entei's ability to potentially burn things like defensive Chomp is also nice, as Azu will only take 21 - 25% from EQ compared to 42.1 - 50% when Chomp isn't burned. The overall less damage taken helps Azu avoid being as worn down by recoil after attacking Chomp.
Defensively, Entei and Azu cover each other well too. For example, Azu dislikes grass types like Amoonguss, Mega Venu, and Tangrowth. Other Pokemon like defensive Skarm and Mega Sciz are also annoying. Entei's ability to take advantage of these grass and steel types by using Sacred Fire is appreciated by Azu. In return, the bunny threatens things Entei doesn't want to take on 1v1, such as Hippo and Gliscor. Azu's ability to threaten sand is also useful, mainly because Tar and Exca are things Entei doesn't really like to face. Being able to scare Heatran is also of note, as it's immune to the main move Entei will be spamming: Sacred Fire. Lastly, Azu threatens several dragons Entei dislikes facing, such as Chomp and Dragonite.
Overall, these two form a nice wall breaking duo. Offensively, they help each other break down checks for one another with their CB boosted attacks. For example, Rotom-W and Slowbro can't take repeated hits from them without being quickly worn down to a point where they can't come in reliably. Defensively, Azu and Entei also help each other deal with steels, grasses, grounds, and dragons for one another. Lastly, both provide a team with strong priority in the form of CB AJ and CB ES. Priority is always useful to have on a team, and the strong ones provided by Entei and Azu are very useful for revenge killing and picking off weakened threats.