ur pkmn will have to be at a really high level (77-85) just so u know. if he hasnt changed pkmn from g/s to crystal they should be espeon, charizard, pikachu, venasaur, blastoise, and snorlax, with most of them beign at level 77 or around and pika at level 81.
"Shiny Typhlosion (Heh so happy about him, he was my starter- without SR )
Poliwrath - Surf
Victreebell - Cut
Pidgeot - Fly
Tyranitar - Possibly Strength
Sycther or Kadabra
What I have now:
Shiny Typhlosion
Poliwag
Bellsprout
Pidgeotto
Abra"
i recomend removing, poliwag, bellsprout, and pidgeotto, keep, typhlosion, abra, and scyther.
recomended moves for typho. thunderpunch, earthquake, fireblast, and some other strong move,
abra, after evolving wait till it learns psychic and recover, then trade it to make it evolve and get it back, teach it dynamic punch and shadow ball, it should stand a good chance vs dark and ghost.
get a normal type such as a taurus, ursaring, or miltank they are pretty strong and cover ur blind spots and reinforce other types. tyranitar is good but as some one already said u dont get to catch one till the end and u catch it like at level 25 or so.
build your team around your main pkmn, thats a very important point in considering what pkmn you should have in a line up, fo ex, get a water typr like gyarados or lapras, that can learn , electric, grass, psychic, fire, rock, ground moves (btw both of them)
but if u decide to keep ur team give balance them, give them protein, carbos, iron, hp up ok level them up by defeating the elite 4, use the old switcharoo, start a bttle with a weak pkmn then switch to a stronger one to share exp. points. good luck if u need any help let me know