Well, I think RuneScape is very basic so heres my suggestion.
First off they should add races such => Orcs,Elves,Night Elves,Dwarfs etc.
Secondly we need more magic spell from different kind such => Necromencer,Basic,Ancient,Summoner,Lunar and an other with a mix of them all.
Thirdly we need Advanced combat style. What I mean there? I mean that its should have an addition to for exemple warrior, Its should be something like => Swordsman,Barbarian,Knight,Paladin etc.
For Mage => Master Mage,Wizard,Demonologist
For Ranger => No idea yet...
Finnally we should have also Advanced Races. Heres some exemples :
Demons,Undeads,Death Knights,Ogre,Troll,Ghouls etc.
You get get an Advanced race by getting cursed by the monster, Its would be a Random Event. And you would have different stage of Evolution. For exemple we will take Demon
1st stage - Little Demon
2nd - Half Demon
3rd - Demon
4th - Arch Demon
And you could get an Advanced combat style by using a training from a Master such : Master Paladin, Master Knight etc.
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I might post it on runescape forums. Do you think it would be nice ?