This is just a basic guide to what gear you should use for maging rex at dag kings. All things can be swapped, this is just what i find best without using guthans.
Slayer darting < Cheapest + Easiest to obtain
Helm: Veracs > Niet > Torags > Zerker > Rune
Ammy: Fury > Glory > Power
Platebody: Torags > Veracs > Granite > Rune
Platelegs: Veracs > Torags > Granite > Rune
Boots: Dragon > Rune > Climbing
Shield: Granite/Obby (Same bonuses) > Rune
Gloves: Barrows > Dragon > Rune > Addy > Mith/Combat bracelet
Cape: Skillcape > Obby Cape > God cape > Team cape
Inventory.This is what i find bes suits me for slayer darting. Slightly more brews than restores, higher def may need less brews and more restores, adjust how you feel.

You will need around
1.5k deaths, 2k to be safe, and 8k minds.
Claws of guthix < Using Void Mace for Autocast.The armour/weapons setup s practially the same, just with a few adjustments.
The aim with this is to keep as much mage bonus aswell as pray and defence. This setup gives you -8 mage attack bonus, however it still works great. I'd advise not using torags plate as that gives yo mage attack bonus -32, however gives more defence. You can play with it how you like, this is just my preferred style.
You NEED a guthix cape this allows you to charge, meaning the ability to hit 30's.Inventory.3k Bloods is advised as well as adequate fires and airs. Other than that, keep the inventory as close as possible to that.
Points.Using slayer dart is a much more cost efficient way of doing this, however kills are much slower and your hit is determined by you slayer level. I believe 60 slayer hits around 16, however not confirmed, at 69 i hit 18s. Less kills per trip than Claws of Guthix
Using claws of guthix is my preferred style, however you have a much lower defence bonus to range, which is highly recommended. On the up side you can charge to hit 30's therefore killing rex much much quicker. You also hit constantly on him with8 mage, i recall hitting a string of 6 numbers over 24 in a row. Only problem is that you use twice as many blood per strike, costng double a slayer dart, but you kill them 2-3 times faster than with slayer dart therfore levelling itself out.
To obtain a void mace simply go to pest control, and use 250 points to purchase it, took me little over 2 hours to retrieve this.
My sources tell me you can get 1k slay darts for 140 slayer points off a slayer master, making it event cheaper t slay dart!
If you are soloing, or going with a hybrid, always make sure to take Rune Thrownaxe. This is to spec the middle stone, if you are with a team, check somebody else has otherwise take it upon yourself to take 1, replace a brew.
Thanks for reading my guide, hope it helped.
I will add routes and where to stand in safe spots, how to lure, and more when i next go to dag kings, this is just a basic gear guide for an upcomming dks event.
Please post anything that may be wrong, and i will sort it out.
p.s i bad speller.
Again thanks.