ofcaurse he or she can level 60tys can heck i can and im level54
by magic
unless you want to die...NO!
in the deep wilderness against greater demon level 92
I would say you should be level 50+. You could be lower but with better food.
erm your supposed to kill Elvarg which is lvl 80+, close to a lesser demon which is also about the same level In melzars maze you have to kill a lesser demon to open a door for a map piece.
Some you can buy at the RC Guild when you have level 50 RC, or you can kill abyssal monsters and they drop them as random drops.
Instantly eh? Well I guess you could kill an abyssal demon for one but you must have 85 slayer though. Another option would be buying off the grand exchange.
The Sword you used to kill the demon with, the sword is good against demons.
You simply right-click them and select (Attack Dark Wizard Level-7) or (Attack Dark Wizard Level-21) Just like a normal monster. If you haven't gotten Silverlight yet do not attempt to kill the Demon.
you need at least a mithril armour to prevent dark wizards to attack you. With silverlight , you can kill it by 1 shot. (silverlight is weakness to any demon , including the demon you have to kill in mezler maze when you do dragon slayer.)
At your level, I would say killing Experiments ( Level 25 - 100Hp = 400exp per kill ) near Canfis.
train kill stuff