Somewhat quick Entei:

Entei @ Choice Band
Ability: Pressure
EVs: 52 HP / 212 Atk / 44 Def / 84 SpD / 116 Spe
Adamant Nature
- Sacred Fire
- Iron Head
- Stone Edge
- Sleep Talk / Bulldoze

Outspeeds Timid Ludicolo outside of rain

Lives:
252+ Atk Landorus-T Earthquake vs. 52 HP / 44 Def Entei: 164-194 (83.2 - 98.4%) -- guaranteed 2HKO
252+ Atk Mega Tyranitar Rock Slide vs. 52 HP / 44 Def Entei: 134-162 (68 - 82.2%) -- guaranteed 2HKO after sandstorm damage
252+ SpA Choice Specs Pixilate Sylveon Hyper Voice vs. 52 HP / 84 SpD Entei: 62-73 (31.4 - 37%) -- 83.7% chance to 3HKO
252+ SpA Heatran Earth Power vs. 52 HP / 84 SpD Entei: 128-152 (64.9 - 77.1%) -- guaranteed 2HKO
-1 252 Atk Life Orb Terrakion Stone Edge vs. 52 HP / 44 Def Entei: 159-190 (80.7 - 96.4%) -- guaranteed 2HKO
68 SpA Ludicolo Scald vs. 52 HP / 84 SpD Entei: 102-122 (51.7 - 61.9%) -- guaranteed 2HKO
0 SpA Milotic Scald vs. 52 HP / 84 SpD Entei: 102-122 (51.7 - 61.9%) -- guaranteed 2HKO
0 SpA Rotom-H Thunderbolt vs. 52 HP / 84 SpD Entei: 60-72 (30.4 - 36.5%) -- 54.6% chance to 3HKO
252 SpA Mega Manectric Thunderbolt vs. 52 HP / 84 SpD Entei: 90-106 (45.6 - 53.8%) -- 41.4% chance to 2HKO
252+ Atk Aerilate Mega Salamence Double-Edge vs. 52 HP / 44 Def Entei: 171-202 (86.8 - 102.5%) -- 18.8% chance to OHKO
252 Atk Parental Bond Mega Kangaskhan Double-Edge vs. 52 HP / 44 Def Entei: 163-193 (82.7 - 97.9%) -- guaranteed 2HKO

Damage:
212+ Atk Choice Band Entei Iron Head vs. 244 HP / 0 Def Sylveon: 190-224 (94.5 - 111.4%) -- 62.5% chance to OHKO
212+ Atk Choice Band Entei Bulldoze vs. 56 HP / 0 Def Heatran: 144-172 (83.2 - 99.4%) -- guaranteed 2HKO
212+ Atk Choice Band Entei Iron Head vs. 0 HP / 0 Def Terrakion: 146-174 (87.9 - 104.8%) -- 31.3% chance to OHKO
212+ Atk Choice Band Entei Sacred Fire vs. 4 HP / 0 Def Ludicolo: 168-198 (107.6 - 126.9%) -- guaranteed OHKO
212+ Atk Choice Band Entei Sacred Fire vs. 164 HP / 140+ Def Ludicolo: 127-151 (72.1 - 85.7%) -- guaranteed 2HKO
212+ Atk Choice Band Entei Stone Edge vs. 0 HP / 0 Def Mega Charizard Y: 408-484 (266.6 - 316.3%) -- guaranteed OHKO
212+ Atk Choice Band Entei Sacred Fire vs. 0 HP / 0 Def Mega Charizard Y in Sun: 114-135 (74.5 - 88.2%) -- guaranteed 2HKO
212+ Atk Choice Band Entei Stone Edge vs. 252 HP / 108+ Def Rotom-H: 130-154 (82.8 - 98%) -- guaranteed 2HKO after Leftovers recovery
-1 212+ Atk Choice Band Entei Sacred Fire vs. 4 HP / 0 Def Mega Manectric: 100-118 (68.4 - 80.8%) -- guaranteed 2HKO
212+ Atk Choice Band Entei Sacred Fire vs. 4 HP / 0 Def Mega Kangaskhan: 126-148 (69.6 - 81.7%) -- guaranteed 2HKO