4th Gen Pokemon D/P team

Hi, I was wondering whether anyone had some good advice for my 6th team member. So far I have Infernape lvl36, Starapter lvl35, Luxray lvl36, (at 4th gym), I will also be getting febas and gible as soon as I beat the sixth gym. I was thinking sheildon. Any suggestions are greatly appreciated. Thanks.

Keep in mind that Shieldon is exclusive to Pearl and Platinum. But either way, I wouldn't recommend it. It doesn't synergize well with your team, as it can't beat any Pokemon that none of your other team members can. In its place, I'd suggest Roserade or Mismagius, as they can learn Shadow Ball and Grass type moves.

As for Feebas, you can find it in the foggy place in Mt. Coronet, but only by fishing at 5 spots, which change every day. Even worse, you have to find those spots all by yourself. If you don't want to go through all that trouble, I'd suggest Gastrodon instead.

I'm with Feraligatr's suggestions. Roserade can be a great option for a Grass-type and a powerful special attacker option. I tend to use it in most games and it usually never lets me down in that.

Also, as he said Feebas is one of the hardest Pokemon to get in Sinnoh. Gastrodon, Golduck, Floatzel and Quagsire can make for a solid alternative for a Water-type.