Hints and stuff

Mr. Mine - for recycle, so you can reuse Used TM, just level it up to lvl 33 and it will learn recycle.

Lanturn or anyone who has Illuminate - best for catching catching pokemon that rarely appears in a dungeon floor like Pidgey. Teach it rest so that if it has any status problem or has low hp it can recuperate. Just take a few blows from other pokemon till it stops blinking.

Deoxys - i dont know why but when i use it in Level 1 dungeons 50% of the pokemon i battled, those recruitable, gets recruited. just bring 4 frustration and a tight belt. Also it has high stats for lvl 1, so it can pretty much survive till you hit the 99th floor. Its not the best candidate though for Purity forest.

Catching legendaries... you can catch them after the credits roll no need for full hp and stuff... you just need a friend bow and in case of mew and the Regis the music box. Mewtwo, Ho-oh, is 99% recruitable after battling them the 2nd time. Celebi is also 99% recruitable.