[3.P] Evil Assaulting a Temple

[CreganTur]

I'm trying to deal with this from a DM perspective. A temple or holy site of great importance is obviously going to have all manner of protection spells (protection from evil) on it, as well as things like Guards and Wards and a number of other spells I'm not thinking of at the moment.

So, what considerations do I need to think of for a group of demons and devils to assault such a place? Is a lot fo dispell magic enough, or is there some other option they could use to break the defensive enchantments so they can enter this holy place?

[Twilightwyrm]

Assuming you don't want to just nuke the place, there are a few options:
-"Espionage and Sabotage"- Get some people on the inside with access to dispel magic, and have them slowly dispel and destroy the defenses. Warlocks would have access to it all day, and could thus work faster, but would be more easily detectable. Clerics would fit in with the theme, but their auras would give them away. I suggest archivists. They have a pretext for being there (magical research), plenty of spell per day to dispel the magic, and can effectively spy on the enemy by "offering their intellects to help solve the problem" once the enemy starts realizing something is wrong and taking counter measures.
-"Siege"- Basically what it sounds like. If you cannot use you amassed fiendish army to immediately break in, you can always surround the temple and clear out the surrounding countryside first, before slowly eating away at their magical defenses with Dispel Magic from the outside (Most demons have Dispel Magic, or Greater Dispel magic at will, so this shouldn't pose much of a problem). Having your Bone Devils and Ice Devils spam Wall of Ice can both help wall in the enemy, and erect fortifications for your troops, all of which can easily be disassembled by the various forms of fire magic available to demons and evils alike, if necessary. Keep in mind that you won't likely be able to starve them out, since at least some of their members can create food and water, and keep in mind that this may enable them to call in extraplanar reinforcements, if given enough time. Best to combine with the following.
-"Artillery/Ariel Bombardment"- The magical wards that keep fiends out, in my experience, do not have the same effect on rocks and fireballs. If you are leading demons and devils, hopefully you can get any Pit Fiends (who have Quickened Fireball at will) or Balors (who have Telekinesis at will) that happen to be with you to lob fireballs and large rocks respectively at the enemy fortifications. On this note, Nalfeshnee demons have Call Lightning for this purpose, Marilith and Vrock demons also have Telekinesis, and the aforementioned Pit Fiends can also create undead from dead enemies to serve as meat shields.
-"Diversion"- First, find out how big of a military force the temple has on hand. Then find a tactically (or emotionally, if many of the families of the members of the temple live there) important stronghold, village, or city nearby that is not as heavily defended. You can do this to many if you have the numbers. Have your entire force move in to attack it en mass, leaving only an undetectably small force near the temple. Either siege it, or capture it, and start committing the more horrifying and (specifically) enraging war crimes you can think of. Make sure the force you have there to siege/hold the area(s) are small enough that they could be defeated by the full strength of the temple's army, but big enough to warrant concern. As soon as the enemy's army starts amassing there, create the illusion your army is still there (some Persistent Images help), and have your entire army teleport in right outside the temple grounds. The temple's military will not be able to get back fast enough to stop you, and you won't have as many defenses, or defenders, to deal with when you easily capture it.
-"Drawing them out"- Similar to the previous one, this relies on you taking a tactically important, and defensibly, site nearby. War crimes are unnecessary in this case, but may help motivate the temple's defenders to act more immediately, giving them less time to prepare. Instead of feinting the teleporting back to the temple, this strategy relies on your drawing their army into the open, where it does not have the defenses of the temple to shield it, and doing battle with it there on more equal footing, or more preferably, from your own defensible area. Remember, if they spring some trap that leaves you at a tactical disadvantage while there, you can always default to the previous option, and for go for a run on their temple.
-"We have one too"- This is similar to the previous strategy, but relies more on audacity and construction. Basically, you have your army teleport in nearby, but instead of attacking, you have it build your own temple (of doom) more or less right on the doorstep of the temple you are looking to take. Your forces will be far more efficient at resource gathering, given teleport can cut down on travel times, and you can simply raid the surrounding area for supplies. Within no time you will have your own looming temple of doom basically flipping the bird to the temple defenders. Bonus points if you start trying to convert away their flock to your faith. This will undoubtedly provoke them to attack eventually, and at which point you can either try for a temple run, or open battle as before, only this way without having to waste troops on taking some other place first.
-"Mix up"- Any mixture of the above tactics. This will probably be your best option, as espionage and sabotage will hep take down the magical defenses, and give you early warning of the enemy forces moving out (your agents might even be able to help get the temple to over-commit troops to opposing your army, leaving the temple defenses even more anemic and reinforcing their "faith" to the temple's cause). Unless you think you have the forces to do both, I would suggest against trying both a temple run and a mass battle. Remember, the point of both tactics is to divide the enemy forces. There is no point in doing so if you are just going to divide your own as well.

[O.L.Scudmungus]

Perhaps find a way to desecrate the holy site? Not by using the spell of the same name, but finding some act that will sully it's holy status.

Typically with any organisation, the families and ties that link members/operators with the outside are a good place to start.

Coercion into forbidden acts, typically under magical/chemical agents followed by subsequent blackmail is another tried and tested tool for manipulating and controlling key members of a system.

You don't have to start at the top - Evil can simply get their hooks into a potential candidate during their formative years and then wriggle them far enough to be in a position to cause the fall of the site.