In the Pokemon video games:
* You'll lose the battle. The game doesn't treat legendary Pokemon any differently than regular ones in terms of how a battle plays out. If they're stronger and you can't defeat them, you lose.
* You may get other consequences depending on the context of the battle. For example, if you're trying to catch a legendary Pokemon, you may have a chance to catch it if it's fainted. Or, if you're facing a legendary Pokemon as part of a story event, losing might trigger a different story path.
In the Pokemon anime:
* You'll likely lose the battle. Legendary Pokemon are often depicted as incredibly powerful and difficult to defeat.
* The consequences can be more dramatic. The anime focuses on the emotional aspects of battling, and losing to a legendary Pokemon could mean losing a valuable opportunity, or even risking the safety of others.
In tabletop Pokemon games (like Pokemon Trading Card Game):
* The rules of the game still apply. Legendary Pokemon have special abilities and strengths, but ultimately, it's your strategy and the cards you play that determine the outcome.
* Winning against a legendary Pokemon can be even more satisfying. Because they are often depicted as incredibly powerful, overcoming one can be a major accomplishment.
It's important to remember that each version of Pokemon has its own unique rules and mechanics. So, what happens when a legendary Pokemon defeats you depends entirely on the context of your situation.