Nothing special happens, the rook is just on the last rank(it is the first rank if you are playing as black). Pawns are the only piece that can promote.
Eigth grade
Then you have a level 70 pokemon!
Death.
The answer is chess.
chess
When a boat reaches its crush depth limit, the inner pressure hull succumbs to the extreme outer sea pressure, causing the hull to implode.
It does not gain any more EXP points and has max happiness unless it was caught at level 100. Nothing special.
Be very good at chess or reduce the CPU's level to the lowest it can be. Winning should be easy if you lower their difficulty level.
chess
horse
it can't go any higher so it's a really good Pokemon (depending on the trainer of course)
Evolution wise, you will get a Croconaw once it reaches level 18 and a Feraligatr once it reaches level 30.