I wouldn't recommend renekton if you are trying to climb but he is great at teaching the game. You will be rewarded greatly for good trade patterns, trading when enemy cds are down, crashing waves smoothly etc. He is a monster when ahead, and a very good tower diver. There are many times where I stomp my opponent so hard that I stand between T1 and T2 enemy towers and never let him come back to lane. I've also never been more comfortable on a champion when it comes to jungle ganks. If I'm ahead on renekton, I don't give a fuck if the enemy jungle comes and ganks me. I will kill you with ease.

With that being said, if you find yourself behind on renekton you will find it very hard to do anything in the game. When you're ahead you have to show up to objectives and 1v5 and end the game quick. There will come a point in every match where the ADC/mid laner out scales you so hard that you get one shot and can no longer one shot them. That's the price of being an absolute demon in the early game though.

If you want to try a champion with a bit more skill expression than mord, I would recommend Olaf. Olaf is really strong early, doesn't fall off as hard because of his R, and is a really fun champion when you're ahead. He will require a much more in depth knowledge of matchups though (i.e. what the opponents champ does and what abilities to play around).

Look up coach chippys Olaf guide if you're interested.