It's the last dungeon in the main plot, if that's what you mean, but there are LOADS of dungeons, some of which you can't access unless you have the right wonder mail. So, really, it isn't.
its marine resort
dark dialga is the last boss in the normal storyline, but in the post game however darkrai is the last boss.
Darkrai
The last boss in Pokémon Mystery Dungeon: Explorer of Time is Dialga. After that boss you get the credits list and it says "The End". But it's possible to keep playing after that.
If u really want to know ill tell u wat i know i think the last boss is darkrai which is in deep dark crater
Buy friend areas. The last dungeon is the deoxys one
Fight Darkrai
Hes the last boss, in dark crater Hint: bring ALOT of reviver seeds since Cressilia will be fighting with you and darkrai has max evasion and nightmre.
49f liar
It is called "In the Future of Darkness."
That is the last dungeon story-wise. There are other dungeons that you can get through wonder-mail though. If you want to get technical, Deep Dark Crater comes after Dark Crater.
I thinkthe last boss you fight with is darkrai but im not very sure.