I’m a D&D 3.5 dungeon master and was playing a session with my players in which they went on a rampage and killed/murdered 100-200 low level soldiers with their spells, in some cases 75 at a time because the men were grouped together. They are now demanding 50 000 xp saying that if they defeat a monster they get the xp so I should give them the full amount they want. I personally don’t want to give them that much, allowing them to easily gain 3 levels, simply because they have area spells. I feel especially bad for the other non magicians who cannot keep up with that much carnage, and will end up lagging behind and get way less xp. Is there a good way to give xp to the magic casters?
The DM can officially overrule the XP chart in this situation
This exact situation is described in the Dungeon Master's Guide, p.39, "Assigning Ad Hoc XP Awards":
Sometimes the XP table doesn't quite cover a given situation. If two orcs are an EL 1 encounter, four orcs EL 3, eight orcs EL 5, and sixteen orcs EL 7 (maybe), are thirty-two orcs an EL 9 encounter? A party of 9th level characters can almost certainly wipe them out with ease. By 9th level, a character's defenses are so good that a standard orc cannot hit him or her, and one or two spells cast by a character of that level could destroy all thirty-two orcs. At such a point, your judgement overrules whatever the XP table would say.
If the DM rules that the encounter was no challenge, they can award no XP. If it was barely a challenge, they can award less XP than the chart would allow. This is particularly the case when fighting creatures whose CR is eight levels or more below your character level.
What is the correct amount of XP?
Supposing you want to award XP by-the-book to avoid accusations of unfairness, be certain that you are awarding XP correctly. As per Dungeon Master's Guide, p.36-41:
- Only characters who take part in an encounter gain XP. The rules agree that party members who weren't present don't get any XP.
- XP awards are divided by the number of PCs. Check whether that 50,000 XP is divided between the characters present or not.
- XP is calculated per-character based on current character level. Higher level characters gain less XP for low-level creatures. In future, lower level PCs will gain more XP to help them catch up.
- Encounters 8 levels below you have no standard XP award. If you're level 10, then CR2 or lower soldiers don't have to give any XP at all.
- Circumstances can affect XP award. You can give two-thirds or half XP for an encounter where the enemies fought at a significant disadvantage which made the fight far easier than normal.
- A character can advance only one level at a time (Player's Handbook p.58). This is per-adventure. The most you can gain is 1 XP short of the next level; e.g. a level 10 character can only reach 1 XP short of level 12.
Double-check that XP value.
Given that 50,000 XP is enough for three levels:
- If that's 50,000 XP split two ways, the characters must be at least 8th level.
- In that case, 100-200 soldiers must give 250-500 XP each. That's possible if they're CR 2 or CR 3 soldiers on average. CR 1 or CR ½ warriors won't give enough XP, and won't give any standard XP value to characters of level 9 or above.
- If that's 50,000 XP per character, the characters must be at least 12th level.
- In that case, with two characters, 100-200 soldiers must give 500-1000 XP each. That's only possible if they're all CR 7-CR 9. That's not really "low-level" compared to the PCs' level, so this situation seems unlikely.
You can't ever gain more than almost 2 levels at a time
Page 58 of the PHB says, in part:
A character can advance only one level at a time. If, for some extraordinary reason, a character’s XP reward from a single adventure would be enough to advance two or more levels at once, he or she instead advances one level and gains just enough XP to be 1 XP short of the next level. Any excess experience points are not retained. For example, if Tordek has 5,000 XP (1,000 points short of 4th level) and gains 6,000 more, he would normally be at 11,000 XP—enough for 5th level. Instead he attains 4th level, and his XP total stands at 9,999.
So they level up, at most, 1 level and all but 1 XP from the next level. They can then kill a rat or whatever and get 1 XP and level up, but they definitely don't level up 3 times, and you can be a jerk about them getting that last 1 XP if you want to.
Full casters will make mundane characters look completely impotent, and will level up much faster in games where not everyone gains XP at the same time
Prepared full casters are tier 1. No class completely without magic is higher than tier 3, and tier three classes without magic generally are from Tome of Battle and can also have magic instead of class features sometimes.
Most mundane classes, especially in games sticking closer to core, are tier 5, though a couple are tier 4. That is a rediculous and massive power difference. That means you are trying to help characters best described as "Good at one rarely applicable thing, or mediocre at one thing, or simply too unfocused." keep up with characters best described as "Can do anything and everything, often better than lower-tier classes that supposedly specialize in that thing." You can't do that. If you are playing West Marshes style in 3.5, magic is power and mage PCs will lord over fighters and rogues without difficulty or the realistic possibility of retribution.