I've been raising a Skorupi to become a Drapion before I challange the E4 in Diamond, but my friend told me Drapion wont help much. Should I keep the Skorupi or replace it with another Pokemon, and which one in that case? My current team is: Rapidash, Empoleon, Bibarel (HM Slave), Murkrow, Gible and the Skorupi ofc.
Let's see know. The E4 is Bug, Ground, Fire (well....) and Psychic. You can easily dispatch the bug E4 member Aaron with your majestic fire steed Rapidash, and Bertha (ground E4 member) will quake under the power of your trident faced suit wearing Empoleon. Flint (the fire E4 member) has some fire types as well as a Steelix. And a Lopunny, and a Drifblim. Yep. Moving on, your Empoleon can take the Steelix, and Murkrow has the type advantage against the Drifblim (evolving it would be good) and Lopunny isn't too powerful so Empoleon could take it. Murkrow can take the Psychic E4 member (Lucian) relatively easily, in the end I see on reason to train up Drapion. It's weak to one E4 member and is out shined by your Murkrow.
TL;DR: Stick with the mafia crow and don't train up the Skorupi.
I think you should not keep Skorupi for elite 4. Your team is quite well for e4. Skorupi is not a good Pokemon for e4. You have already Fire, Water/Steel, Normal, Dark/Flying, Dragon/Ground types of Pokemons. I think you should evolve your Gible and Murkrow first. It will increase their powers. You should train a Normal Pokemon like Blissey , a tank of hp or train a Gyarados for e4. I have also a Gyarados but I play PRO. For Gyarados,
Hold Item: Liftovers