Trade it while it is holding a Protector.
evolve a ryhorn, trade for one, or CHEAT! XP
it evolve at lv42
give it poo
give it a protector and trade it
Around lvl 40-50 depending
You can get Rydon to evolve by trading it with a protecter.
trade it into Pokemon emreld
Rhyhorn evolves at level 42.
you can evolve rydon by trading with the protctor
give it to rydon and trade it to make him evolve
You can't do it in ruby. You can only do it on diamond, pearl, platinum, heartgold, soulsilver, and any others after that!
Rhydon doesn't evolve at one set level, you must trade it while it is holding the protector.