To expand on this, DnD 3.5e has the diplomacy skill, which is used to change the attitudes of NPCs you interact with. Usually this skill is only feasible to modify the attitudes of NPCs by one step (say, an indifferent bartender to friendly, or a friendly authority figure to provide aid). You generally cannot use the diplomacy skill more than once on the same NPC, at least within a short period of time (without anything notable happening which may change his opinion of you), even if you succeed on the initial check (to prevent gradual brainwashing of NPCs from one step to another).

This skill is also highly impractical in combat, as diplomacy checks usually require a minimum of 1 minute (10 rounds) during which your opponents are free to pommel you and your friends.

However, a character with optimized diplomacy can do all sorts of ridiculous things like, say, convincing a bunch of hostile orcs to drop their arms and lead you to assassinate their warchief. And all within one turn, since you can rush diplomacy checks if you can afford to take a -10 penalty.

Doing so require hitting effective DCs of 50 or 60 (depending on whether the check is rushed or not). What it means is that the player has to roll a combined total of 50 (or 60) or higher by rolling a twenty-sided die (d20), plus whatever modifiers he has. A standard character with max skill ranks in diplomacy can usually only achieve a +30 modifier at max level (20) or so, making this feat (without rushing) nearly impossible unless the character rolls the maximum result on the d20.

Diplomancer builds push their diplomacy skill modifier to ridiculous levels by taking advantage of skill synergies, class features which allow them to count more stats to boost diplomacy checks (or count the same stat twice, like the Marshal's aura), spells, enchanted magic items, etc. IIRC there was a Diplomancer build they could reach a modifier of +58 by level 6, WITHOUT using any magic items.

Yep, this is exactly on par with what pacifist Frisk does.

Some builds, like the jumplomancer, take classes (like Exemplar) with the class feature to substitute one skill check for another. The popular choice is Jump. Or Perform. Sounds familiar? (see Mettaton fight).

Things get really broken when jump is used to substitute for diplomacy, since the former can be pushed far more easily by stacking speed bonuses. Hit a DC of 150 (or 160 for rushed), and you can turn the aforementioned hostile orcs into your personal ISIS squad fanatic followers. And by jumping really, really high, if I might add.

Yeah, it's like magic. Except better, because they don't get to resist it, or counter it with other spells (unless they deafen themselves or something so they can't hear you speak, but skill substitution takes care of that as well). You basically talk so good (or jump high enough) that you geass every person you meet without using any magic.[/spoiler]