Entei locations — where to catch

In Paldea (Scarlet & Violet)

• East Province (Area Three) — Static Encounter

In Johto & Kanto (HeartGold & SoulSilver)

• Roaming Johto — Roaming

In Kanto (FireRed & LeafGreen)

• Roaming Kanto — Roaming

In Johto & Kanto (Gold, Silver & Crystal)

• Roaming Johto — Roaming

Other games (8)

• Brilliant Diamond / Shining Pearl (Gen 8): Johto
• Sword / Shield — The Isle of Armor (Gen 8): Max Lair
• Ultra Sun / Ultra Moon (Gen 7): Ultra Space Wilds, Ultra Space
• Omega Ruby / Alpha Sapphire (Gen 6): Trackless Forest
• HeartGold / SoulSilver (Gen 4): Johto
• Fire Red / Leaf Green (Gen 3): Kanto
• Colosseum (Gen 3): Mt Battle, Realgam Tower, The Under
• Gold / Silver / Crystal (Gen 2): Johto

Entei — full Pokédex entry