So, I was replaying BW and out of curiosity skimmed through Serebii

>>27817177
It's a failsafe. If you boxes are completely full when fighting N, you'd be forced to catch the dragon, but with no PC space the game wouldn't allow the capture. Since the scenario was unlikely, but could lock people in an inescapable loop, they programmed it where if you beat the dragon with a full PC, you could continue the game without catching it. Then after beating the game, it would appear on top of Dragonspiral Tower like how N caught his dragon. I think the level changes, and people thought this was a way to break the shiny lock the Gen 5 dragons had, but it didn't.

>>27817177
It just means that if you're literally maxed out on capacity and you physically can't catch the dragon, it'll show up there and be rebattleable.

Same as any other overworld legendary, talk to the sprite, "GAAAAOOOOWR", battle begins.

>>27817631

Oh, I know it's a failsafe - I was just curious about how it plays, if it was a generic interactive Pokémon or if anything else appeared.

>>27817659

Ah, nothing besides that then? Alright.

The game doesn't even have any alternate dialog. It still acts like you caught the thing.