It depends on who you ask. A kid will say Arceus. A competitive player will say Miraidon. A troll will say Shedinja.
The strongest Pokémon is the one you use well. A perfectly trained Magikarp can’t beat a badly played Rayquaza, but a pro player with a Pikachu can wreck an amateur with a box of legendaries. Skill beats raw power.
Or, you know, just pick Primal Groudon. It sets up permanent sun, negates water moves, and hits like a truck. It’s been terrifying since 2014. Some things never change.
So next time someone asks you this question, take a sip of your coffee. Smile. Ask them: “In what format? With what rules? And are we counting the fact that Bidoof is technically a god in the Mystery Dungeon games?”
They’ll have no answer. You win. And that’s the strongest play of all.