Melee till they are not aggressive. Subsequently Range/Mage Safespot. Any shield I can wear besides the anti dragon shield? I'll have all my equipment in my inv. I'll also take a prayer urns. Could this be great XP too? Should you use urns for RuneScape gold every skill?
To start with, you should ideally use Ranged and Melee, if your melee stats are anywhere near acceptable (80+ Strike 80+ Power ). You could try magical - it may turn out to be effective - but in general it's expensive (200GP per throw using the Polypore is still expensive, relatively).
Second, utilize higher-defence armour until you become proficient at Prayer shifting at TDS, then switch to Void. How would you be good at prayer changing? If they are attacking with melee and they roar then you've got to guess involving variety or mage. If your guess is right then it's good but if it's wrong then you are likely going to take damage before you change again...
Correct me if I am wrong... it's just what I read on manuals I never went to there or even done the quest yet. That is how I do it. So it is a pattern and they don't just switch their strikes randomly, right? Nah it is arbitrary, it is just that they don't actually hit with melee in any way, so it's better to plead agaisnt magic or variety. If they are going to start ranging, if they roar, a little bone shard item will seem, and move upward, even though it can be a little tricky to spot sometimes. Keep a watch out when the demon's simply been meleeing.
At slayer tower you'd kill them quicker with Buy RS gold melee so if that's what you need go with that path. Armor should be your greatest magic defense (Strike is melee but it's defense relies off magical so d'hide and so on ) or in case you really feel like praying (Bit of a waste unless you're fighting the mutated ones with a cannon) then greatest prayer protection and pray protect melee. For weapons go with your best slash weapon.