The D&D 3.5 E6 variant rules cap character's level progression to Level 6.
How does this affect high level magic? I understand that spellcasters may continue to add more spell slots once they reach Level 6 by purchasing special feats with their accumulated XPs.
However, are spellcasters limited to casting only those spells available at character Level 6? This would mean for clerics, sorcerors, and wizards, all 4th+ level spells are off limits.
Stuff like angels, demons, and dragons might be able to manage such feats of magical prowess, but your humans, dwarves, and elves cannot. Eliminating 4th-level and higher spells from the game is actually the point of E6 – while all spell levels tend to have fantastically efficient options, 4th-level spells is where it starts to get into the “there is no answer to this without magic” region.
For example, grease or glitterdust may be much more potent singular actions than anything a warrior can do, but a warrior can avoid the grease, make the glitterdust save, have ranks in Balance or the Blind-fight feat, and so on. There are answers. If you drop solid fog on a mundane warrior, he’s just out of the fight for several rounds, and there’s basically nothing he can do about it.
Certain, select 4th-level or higher spells may become available to the players at the DM’s discretion, but these are always going to be plot devices – artifact-grade items provide them, or lengthy and complicated rituals are necessary (quite possibly requiring side-quests to gather the necessary materials). But the players never get 4th-level or higher spell slots to do with as they please. There are a few tricks that, by strict-RAW, would allow them: it is strongly recommended that these get banned from the beginning of the game.
It is possible, through extreme effort, to gain the ability to cast certain 4th- and 5th-level spells in E6.
This thread details this process (it's complicated) and the resulting available spells.
Here is a short summary, though:
The siphon spell from Complete Scoundrel will allow a caster to burn through a 4th-level wand to get back a 4th-level spell they have cast today (if they prepare arcane spells) or regain a 4th-level spell slot. We care about the former, since you can't regain a slot you never had. By using Versatile Spellcaster (RotD), a character can cast a 4th-level spell by burning two 3rd-level slots, then use siphon to get that back. Then, after getting two 4th-level slots in this way, can burn them to cast a 5th-level spell. This will also require 10 slots from a 4th-level wand, so it's expensive and tricky to pull off.
For clerics, they can use Spontaneous Domain Casting (PHBII) to become able to spontaneously cast spells from one of their domains instead of cure spells. Through Versatile Spellcaster, the ACF, a way of casting arcane spells (Magical Training or a level of another class), and the Alternative Source Spell feat (Dr325), a cleric can gain access to 4th- and 5th-level spells of a specific singular domain.
For fixed-list spellcasters, they can use bloodline feats to access their next spell level, then use a similar combination of effects, allowing them to cast 4th- and 5th-level spells off of their focused spell lists.
Finally, artificers can create scrolls and wands of 4th-level spells out of the box.
The general point of E6 is to limit this kind of magic and scale the general power of effects down. While that magic is often a good thing to have in the world (as a plot-level thing, rather than a player-accessible thing), it can potentially warp campaigns and cause problems if you're going for a certain style or tone.
As listed in this (currently accepted on this very question) answer, E6 is not about this. The plot magic handbook is entirely an exercise of seeing what's possibly by the rules as a tool for both DMs and players, rather than a list of things that should be used or accessible.
If the group is okay with it, player characters can definitely get access to 4th- and 5th-level spells. NPC characters probably should be able to as well, rarely. I personally really enjoy the flavor that results from simply applying the rules-as-written to this magic:
A master cleric, a priest and mage of the highest degree who's dedicated a lot of his life to learning not only how to perform this ritual but how to cast arcane magic as well, can work in tandem with a an allied master of magical engineering to use a complex combination of magics that allows them to cast a single spell, the likes of which the world rarely, if ever sees.
It just feels like a wonderful plot hook and thematic addition, though it may still clash with one's expectations of what a powerful mage can or should do.
Here's some specific examples of what I mean:
And so on.
The point of E6 is actually excluding high-level spells from the game. Because they break the game, because it is hard to do anything against (some of the) 4+ level spells without other 4+ level spells to counter, which forms that huge gap between casters and non-casters, making normal 3.5e and Pathfinder games very "unfair" starting at 7th level, where prepared spellcasters get their first 4th level spells normally. Quoting KRyan's answer about purposes of E6:
Lower-level spells are undoubtedly powerful, but for the most part, they can be handled or mitigated by a lot of characters—characters with good Reflex and Balance can ignore grease, characters with capabilities that benefit fighting blind are much less affected by glitterdust, fly is a relatively short-duration spell, and so on.
This becomes less true with 4th-level spells. Solid fog allows you absolutely no recourse unless you can teleport. Enervation is extremely difficult to defend against (unless you have death ward, which is also 4th-level), and absolutely devastating in effect. Divine power allows a cleric to basically turn into a barbarian on top of his spellcasting. Dimension door and freedom of movement are the beginnings of spellcasters’ “get out of jail free” cards. Polymorph is just basically cheating. And divination, lesser planar ally, and scrying can completely change the nature of game.
And, of course, you might look at that and say “well yeah, 4th-level spells are better than 3rd-level spells; that’s how things are supposed to be.” But the real problem is that non-spellcasting classes do not get any such power bump. What 4th-level spells offer are a series of attacks that are exceedingly difficult to defend against without 4th-level spells, as well as a series of defenses that are exceedingly difficult to penetrate without 4th-level spells. The rogue gaining another +1d6 sneak attack damage, the barbarian gaining DR 1/– (the fighter and the ranger getting literally nothing), those are just small incremental improvements, not a whole new league of power the way 4th level spells are.
And it gets worse, much worse, from there.
But it doesn't mean that it will ruin your game: if you carefully choose which spells are allowed and which are not, it may add an interesting flavour to your game, making your spellcasters feel really epic without spoiling fun of other players.
There is a guide by Forrestfire on GiantITP.com called "High Priests and Archmages: Plot Magic in E6". This guide introduces two terms for characters built in a way to allow using 4 and 5 level spells in E6 rules: "High Priest" for a cleric, and "Archmage" for an arcane spellcaster, hence the guide's name: it is generally full of fluff text which might be fun, but I will try to develop the ideas mentioned in this guide, concentrating more on the RAW aspect of achieving the needed results.
As noted in the guide:
The artificer can, out of the box, begin to scribe scrolls and make wands of 4th-level spells off of any spell list, starting at 5th level. This means that many options, such as reincarnation or animate dead, are available to them at a cost of gold, experience, and time.
According to that guide, the following trick may be performed.
Use the Versatile Spellcaster feat. The Prerequisite is "Ability to spontaneously cast spells", which all Clerics qualify for, being able to cast either Inflict or Cure spells spontaneusly. Feat text:
You can use two spell slots of the same level to cast a spell you know that is one level higher. For example, a sorcerer with this feat can expend two 2nd-level spell slots to cast any 3rd-level spell he knows.
The intended feature is most likely burning your unneeded low-level spell slots to cast spells you actually have access to, but we are breaking the game, so it's not important, right? Let's check if a 6th level Cleric may actually know any 4th level spells... Quote from Cleric class description from d20srd.org:
A cleric may prepare and cast any spell on the cleric spell list, provided that they can cast spells of that level.
That is almost exactly what we need. Not specified that the spells are known, but certainly available. So, we can most likely combine two level 3 spell slots and can cast one level 4 spell, and hence, according to the quote above, we can deploy it after preparing it.
However, we also know that our Cleric needs one hour to fill their empty spell slots with spells:
Each cleric must choose a time at which he must spend 1 hour each day in quiet contemplation or supplication to regain his daily allotment of spells
So, you need one preparation session to get your spell slots back. Then you combine your regained 3d level slots and prepare a 4th level spell in another meditation session, you are allowed to have as many of those as you need.
This gets considerably harder.
You need to convert four level 3 spell slots in two level 4 spells: your normal two 3d level slots you have at level 6, your Domain 3d level slot, your bonus slot for Ability score (Wisdom 16+ needed). Cast those two spells, you need them used, not ready.
Versatile Spellcaster feat doesn't convert 3d level spells into 4th level spell slots, it only allows you to cast and prepare level 4 spells. How do we get those 4th level spell slots? We need the Siphon spell! RAW, it allows you to spend 5 charges from a Wand containing at least 5 charges of X level spells "to replace spells you have already cast". Notice this very important line:
If you prepare arcane spells, you can regain any one spell of the affected level that you have already cast that day; if you cast spells spontaneously, you can regain a spell slot of the appropriate level.
You still remember that all of the Clerics can cast spontaneously? So, after casting our two 4th level spells, we can spend a total of 10 charges from a 4th level Wand to get two 4th level spell slots. The Siphon spell itself you have to get from a scroll or a wand, and you will have to roll an appropriate Use Magic Device check, as Clerics don't normally cast spells from Wizard/Sorcerer list. 10 charges of a 4th level spell Wand cost 10/50*21 000 GP=4200 GP, a charge of Siphon costs 11 250 GP*1/50=225 GP.
It actually turned out that this part of the loop has limits, as a 6th level Cleric doesn't normally have level 4 spell slots, they have nothing to regain. Some other means of converting 4th level spells into 4th level spell slots needs to be found. You still have the ability to cast 2 4th level spells as a level 6 caster, which is already powerful. Sticking with 4th level spells is also free in terms of money. Or you need to stretch the wording of "regain" a bit.
Notice, again, that you need:
You don't need points 4 to 6 if you are satisfied with casting two 4th level spells (no 5th level).
Your GM has plenty of buttons to disallow that if having no desire to see 5th level spells in his campaign. But even if you happen to persuade them successfully, remember, again, that it was actually the point of E6 to throw high-level magic away. Such a trick is a lot of effort, and it may make for an interesting story hook -- perhaps a whole session dedicated to reviving your Paladin who died at the end of previous session by Raise Dead! Need to deal with a negative level, though, so you can cast Restoration the next day by burning two of your 3d level slots for one 4th level spell.
As soon as Druids also cast spells spontaneously (Summon Nature's Ally) and hence also qualify for the Versatile Spellcaster feat, they may also perform the same abuse as the Cleric to cast a 5th level Druid spell. Or simply stop at 4th level and cast Reincarnate (though this might be "a bit" risky, it is 5 times cheaper in terms of materials, and you don't need 10 charges of a 4th level Wand, the Siphon spell and stretching word meanings).
Pretty same abuses, but let's just check that they will have access to 4th and 5th level spells that way:
Dread Necromancer:
When a dread necromancer gains access to a new level of spells, she automatically knows all the spells for that level given on the dread necromancer's spell list
Warmage:
When a warmage gains access to a new level of spells, he automatically knows all the spells for that level listed on the warmage's spell list. Essentially, his spell list is the same as his spells known list. Warmages also have the option of adding to their existing spell list through their advanced learning ability as they increase in level (see below).
Beguiler:
When you gain access to a new level of spells, you automatically know all the spells for that level on the beguiler's spell list. You can cast any spell you know without preparing it ahead of time. Essentially, your spell list is the same as your spells known list. You also have the option of adding to your existing spell list through your advanced learning class feature (see below) as you increase in level.
To cast a 4th level spell, you have to learn it in the first place, which doesn't happen normally until you get to 8th level. But you can buy a Page of Spell Knowledge (costing 25 000 GP) and learn one spell, then, with the help of the same Versatile Spellcaster you will be able to cast it 2 times per day (by burning all of your 3d level Spell Slots. Well, 25 000 GP is a lot for E6 characters... Why not just play T1 guys if you are looking for a way to break the system?
You can use the advanced slots for metamagic, though, not paying for the Page of Spell Knowledge.
If you are OK with that way of playing, why don't you just go further and modify E6 to stop at 8th level or simply play the game normally, advancing without E6 rules?
There is no resurrection available to PCs in E6 under normal circumstances, that makes life a valuable thing. There is no teleportation available either -- makes sense for castle walls to exist, and so for ship, post-houses etc. No Atonement means that it is very important for your Paladin to adhere to their guidelines -- etc.
Each 4+ level spell can make your game less meaningless by excluding one more problem from it -- and D&D is actually a game about solving problems by making decisions.
As soon as E6 is compatible with both 3.5e and Pathfinder, I have some Pathfinder entries in this answer.
