So I have completed all 36 mage tower challenges and I can say without a doubt the absolute hardest is the prot paladin one. The simple reason being the more hp the boss has the more rng involved. Now I beat some of the tank ones in literally 3-5 tries. The demon hunter and monk ones are stupid easy and I have no idea how to even play those specs (monk gets an auto-win pet that does all the work ur just a dps.) The prot paladin one took me almost 8-9 hours straight and maybe close to 80-90 attempts who even knows. I had many 1-5 mil wipes just one gcd off killing it. So how did I make it as easy as possible?
First of all talents:
Blessed hammer
First Avenger
Fist of Justice
Cavalier
Hand of the Protector
Consecrated Ground
Last Defender
So the big difference is Last Defender instead of Seraphim why? if u clump the adds on the boss and dps it u get a pretty big dmg increase. Seraphim just fell flat for me I know many people used it but it's not as good imo.
Consumables and Gear:
Legendaries I only have two on most of my characters besides my main since i have 12. So I had pryaz and the retribution divine storm chest which does nothing but Legendaries don't matter much. What matters is using the heirloom strength trinket from WoD Gronntooth War Horn. When u kill the eyes and stack the adds and keep killing them u can have a 75%+ uptime on this so that's bascially a straight 10% dmg boost on the bosses which is huge!
Bear Tartre Food is something people know about and when u kill a mob u get a speed boost so def use that. Beside that a strength flask and defile rune if u want to but I didn't need it. My ilvl was about 917 equipping the Gronntooth and 923 without no tier or good trinkets. Lastly Goblin Glider no matter how good you think you are just take it and use it you can make 1 mistake and be knocked off it's a life saver. On the attempt I killed it I never got knocked off but still use it.
Strategy:
Phase 1:
So the big problem is the infernals right? Well the strategy I found to almost NEVER getting knocked off is constantly running in a circle and jumping. It sounds silly but If you keep jumping and circling the boss you will most likely dodge all their strikes. You can turn your back to the adds, to Kruul, to the infernals it doesn't matter. Do NOT treat it like normal tanking with good positioning just KEEP MOVING and JUMPING. Jumping is really important in P2 because u can potentially save yourself a tick or two of the goop and if you always keep moving you can avoid it. I avoided SO much damage by doing this in P2.
The next issue is the nether horror adds and how to pick them up and deal with the infernals at the same time. Wherever velen is just drop a consecration on him when the adds come out and run away from any infernals the adds will automatically come to you and you can cleave them with the boss with Last Defender's buff + the Gronntooth trinket constantly staying up. When you get too many stacks just use an orb. Orbs actually despawn so it's better to use them then try to save them. I went into p2 with no orbs. It's better to do more DPS then try to be clever and save orbs.
The eyes either avenger shield them or judgement + shield of the righteousness. People say to ignore them but that's a bad idea because you will be overloaded. Plus with this strategy it can constantly keep up the 10% dmg buff and Strength from Gronntooth.
The stacking debuff decay, let it go till 6-9 and when it has 7 seconds ish left just stun the boss and go kill an eye or consecrate where the adds will come out and don't be afraid to avenger shield the adds to get them a little low so their debuff doesnt get to high. You really dont need to silence the boss too much only at important points when the debuffs get high otherwise throw around ur avenger shield at eyes or nether horrors.
Now Kruul and P2:
So when he lands having adds is actually a good thing because of last defender but don't worry if u have them or not! Unlike other specs where they cast their aoe. The goal with Kruul is to kite him in a circle around the place not in the middle and constantly move and jump. Do not go near any infernals and be ready to interrupt. Now the other reason Last Defender is so good is u can spam Shield of the Righteousness and pre-soak his annihilate while moving to avoid the green aoe.
So I had 5 annihilate my prot paladin is actually my LOWEST geared toon but I don't know if you can only have four maybe with mythic gear.
How I soaked:
So first rule is whenever an annihilate comes up make sure you are topped off with yourself heal or an orb. The second rule is to always pre-use shield of the righteouness. The reason is he can stomp u and cast the annihilate if ur constantly moving u can mostly dodge the aoe but don't have time to ALSO shield of the the righteousness.
1st Shield of the Righteousness
2nd Shield of the Righteousness
3rd Guardian of Kings + Shield of the Righteousness
4th Argent Defender + Shield of the Righteousness (even with this let's say an add hits you and then he stomps you could die so always shield!) and after defender use urself heal or even lay on hands u can use an orb and stun to delay the 5th for 30 seconds
5th Blessing of Protection
And he should be dead shortly after!
I hope this helps you guys get it I know it's the hardest one but if you constantly keep moving and jump the parts you struggle on should become easy and then with good RNG on the orbs you should be able to get it! Good Luck