The most comically, hilariously, overpowered skill in 3.5 D&D was a skill that very few classes got, could only be used trained, couldn’t be used reliably and had a drawback if you ever rolled a natural 1. It was also something that wizards didn’t tend to care about having, clerics could almost never take advantage of, and if you had access to it, would take over your build because of what it let you do.
It had a stupid name too.
It was Use Magic Device.
The 3.5 skill system had some peculiarities, and most of them made it fiddly. At every level, you got a number of skill points, based on your class and intelligence modifier. Higher intelligence, more skill points. These points could then be spent on a number of skills, which then improved your ability with those skills when you wanted to do them. If your class was good at those skills, they were class skills, and you could buy them at a rate of 1 skill point for 1 skill point. Oh that’s confusing? Well, you’ll get used to it. If you weren’t getting that class advantage, to level up a skill by 1 point, you needed to spent 2 skill points, and these were known as ‘cross class skills.’ Class skills could have a maximum number of ranks of Your Level+3, and Cross-class skills had half that. Similarly, skills could be class exclusive, they could be trained-only where if you didn’t have skill points invested in the skill you couldn’t even attempt it, and they had skill synergies, where if you had 5 or more skill points in a thing, you got a permanent bonus to another skill.
This system’s fiddliness comes when you need to do batches of handle things across multiple levels of different classes. A level 5 rogue’s skills were simple, if varied, but a level 3 fighter/level 2 rogue could have a very different time of things, complicated in no small part because the fighter sucks and fighter 3 sucks the most. I don’t remember playing with Dungeon Masters who weren’t willing to hand-wave these specific rules and simplify it by saying if it’s a class skill for you, it stays a class skill, and tracking the way the caps can change and the cross-class skills work was less demanding. This also made taking class levels of (for example) Fighter less punishing, because hey, you already had it hard enough.
Most characters didn’t care that much about their skills; you would pick three or four things your class was good at and focus on them, with some real dog skills like ‘climb’ (remember, characters wind up flying in this game) and ‘jump’ (unless you push it to the limit, this skill doesn’t do much for general application), and ‘scry’ (which you won’t be able to use until you have a level 5 spell). On the other hand, Sense Motive and Diplomacy could be used for very powerful effects and Tumble, god, Tumble was worth having a single skill point in even if you didn’t succeed at the checks, for reasons not worth interrogating at this juncture.
For this reason, no two skill points were truly equal, and getting 2 a level or 8 a level was not just a matter of variety it was also a matter of unlocking huge amounts of game mechanics.
And Use Magic Device was the most busted skill of all, for reasons that did not look obvious at all when you looked at it in the rules. In fact, it looks kinda unimpressive at the start.
What Use Magic Device (abbreviated on forums as UMD) let you do was ‘fool’ magical devices into thinking you fulfilled requirements. This was a way that a rogue could, for example, unlock a door that was sealed with a wizard’s magical rules, if you didn’t have access to a wizard to do it for you, or someone in the party who really liked doing Sudoku and was willing to participate in the Dungeon Master’s puzzle reward system. It almost looks kind of innocent at first, with ideas like ‘activate blindly’ getting you a comical explosion face kind of visual gag.
Where it gets wild is the next step: if you have Use Magic Device you can use a wand – any wand – by passing a DC 20 check. Wands are what we call ‘spell trigger’ items. You use a wand and it will fire off a copy of the spell stored in it, as if you had cast it. They’re also really cheap, and come with a large body of charges. You could buy a wand of 50 charges of a level 1 spell for 750 GP. This meant that any sufficiently useful 1st level spell could be yours if you bought it, then could make a DC20 check. That’s pretty powerful, just in terms of raw versatility. You could also do scrolls, which were even cheaper and more available at the low level, with a DC of 20+the caster level. That meant when you fired off a spell with a scroll, you cast the spell as if you were a caster of the level of the result minus 20, and many spells scaled up based on who cast them.
So the spell Divine Favour is a 1st level spell. You can buy a scroll of it for 15 gp. If you cast it at level 1 (DC 21), you get a +1 to attack and damage rolls, which for a level 1 character is pretty meaningful. But if you hit a DC 26, you get a +2/+2 and if you can manage a DC 29, you get a +3/+3. And that’s, again, for 25 GP, at a point where people may not have any meaningful buffs. That’s not even accounting for utility spells like Knock, Enlarge, Disguise Self, Sanctuary, or Hold Portal, all of which become things that the rogue can do with money and a skill check.
You get more money than you get of any resource in the game. Converting money into other powers is immensely powerful.
But we’re not done yet.
Wands aren’t the only Spell Trigger items. There are also Staffs. Staffs are meant to be cool wizard toys, kind of like a multitool you store a bunch of spells in and then fire off later, and because of this, they need to be better for more powerful wizards. So while a wand does the least version of its spell, with the lowest caster level and lowest ability score, staffs will track your own caster level if it’s higher and your own ability score if it’s higher.
But hey, you’re a rogue, you might not have a great Intelligence. So if you get a wizard’s staff and use your Use Magic Device skill to make it fire off, you probably won’t get a high DC, right? Hey, you might not even have a high enough intelligence to use it!
… well, Use Magic Device anticipated that, and lets you make a Use Magic Device check to emulate a higher ability score for magical items.
This means that you can emulate a high mental stat and high caster level to fire off a staff’s spells. And you’re probably a rogue, a thief, capable of melee combat just fine, you don’t need this as your primary thing. This is a skill you picked up and are boosting with magical items, but it’s very cheap to do so. The skill system is such that you’ll be reliably generating 30s and 40s with the skill checks you care about, which means that now a (say) level 7 Rogue is wielding a staff like a shotgun that they can make pump out fireballs as cast by a level 12 wizard with an intelligence of 25.
And this is with a skill check.
“Ah,” you may think cleverly. But what if the rogue never gets access to those magic items?
Well, Use Magic Device lets you emulate class features. LIke, say, the abiltiy to cast spells, to fulfill other obligations. So a rogue can take feats like ‘craft staff’ and buy scrolls, then pump those scrolls into a staff, and do it all with the same skill. Any investment in gear or items or stats that improve UMD make UMD checks better, because you can use UMD to make buffs for UMD, and UMD then lets your rogue, or warlock, or Bard, or anyone who fights to get the skill play in this space of a feedback loop.
Now, just to clarify, I never saw a player do all this in a game because it’s so obviously over the line.
Kinda funny that the most powerful thing a non-wizard can do is fake being a wizard better than the wizard.
Oh and there’s an entire class built around using this, called the Artificer, but that’s for another time.