The natures determine how a Pokemon grows, for more info go to: http://www.psypokes.com/lab/natures.php
that depends on the moves, the levels, and the natures.
Every Pokemon since the 3rd generation games (Ruby/Sapphire/Emerald) has a nature. If there are no natures, you're playing a 1st generation (Red/Blue/Yellow) or 2nd generation (Gold/Silver/Crystal) game. Those games don't have natures for Pokemon.
Aggron and Rhydon are definitely the best Pokemon on Pokemon Ruby! Their big, strong and both are great and they're awesome!
I don't think so, maybe if natures matched up it would but I doubt it.
Groudon is the best Pokemon in the game that is cachable.
There are many different ways that natures affect Pokemon. For a complete list, try Neoseeker.com and look through Pokemon cheats. You should find everything you need there.
groudon
cranidos
You'll need Pokemon ruby. If you mean ruby to sapphire, then you'll need both games, two gba's, and a link cable.
The best Pokemon in ruby to get without a cheat code is Rayquaza to findo out more about Pokemon go to my website called www.miquel.ning.com.
there is no best base
mudkip