What about Chaos elemental?
Well first release 45 wild and above, by making the wild gate work or slashing webs possible to get there from ardougne lever.... or by making obelisks work.
Then code the Chaos Elemental by making it have 3 attacks
that can deal either magic, ranged, or melee damage - it is impossible to distinguish what damage is dealt until the attack hits.After that add its two special attacks.
The first one teleports players a short space or several spaces away from it. The second attack unequips items that players are wielding, forcing them to take time to re-equip their armour and weapons before continuing the battle.Since we don't have barrow items nor any good weapons, I'm sure no one would even get close to killing the Chaos Elemental...