here's some tips for Mew:
after floor 36, hold an x-ray specs and search EVERY FLOOR up to 98 THOUROGHLY! (i think i spelled it right
) then hold ur friend bow as soon as u see it. be sure to defeat EVERY foe u can, it could be disguised as a different pokemon since it has the move transform. also make sure ur leader is at a high level, the higher ur level, the better the chances. lastly, never give up! it took me 3 tries before i could recruit mew. plus after u recruit it, u get warped out of the dungeon automatically.