pokemon soulsilver elite four?

Well, there's four Elites before Lance.

So;

first there's Will. He's a Psychic-type trainer, so stick with your Gengar and Feraligatr with him.

Next is Koga. He trains Poison-types. I would suggest teaching your Gengar Psychic.

Then Bruno. Stick with your Pidgeot and Gengar (However, on his Onix use your Feraligatr.) Seeing as Fighting-type moves do not affect Ghost-types, Gengar would not be affected. (Remember to teach it a Psychic-type move.)

Karen; Dark-type. I would say use your Ampharos' Rock Smash, but that's a very weak move (Power of 20.) so just try and even it out with all of your Pokemon (Besides Gengar, it will be very useless against Dark-types.).

Finally, Lance! The Champion who uses those feared dragons. Remember to heal your Pokemon to full health before engaging in battle. Use your Feraligatr on all of them except the Gyarados. Send out Ampharos for that one.

Hope this helps...