The other day my player character asked: 'what does my patron want?' - i had to admit, it was a good question. This triggered a cascade of yet other very valuable queries:
These were all good questions. In fact, a bit too good - they had no answers in any of the books in any of the editions. It honestly makes no sense that a demon lord (or any equivalent power) would have both the time and spare energy to dump Infinite Heroic Power on one ultra-weak pion with no questions asked. Yes, it is suggested that the Dungeon Master has to make up (or at least moderate) this - but no outline is given.
So, today we change that.
You do not start off with a demon lord or arch-fey. Instead you make a connection with some powerful entity that is around your challenge rating - perhaps a bit higher. This need not even be an extra-planar creature, so long as it has clear and obvious connections. A hag would have both the time and the interest to hook you up with the right fiend. A dryad would release you from captivity should you make an appropriate 'gift' or offering to their High Princess. A paladin's triad, finding you guilty in that Circle of Truth would be more than happy to relay your conviction and sentencing to the Infinite Oracle when you successfully claim that you wish to mend your ways. In each of these circumstances they would not pass you on to the next step until they were sure you would not embarrass or humiliate you in front of their superior's superior.
This progressive 'contract ownership' need not ever go smoothly.
Contracts get bought, sold, lost, duplicated, bent, folded &/or even mutilated. Contract owners face similar concerns. Which brings us to the next question:
There is only one true limit on what the contract holder could ask for - this pends on the relationship between the DM and the player. As such, even a lawful and good owner could ask for these things, pending their circumstance:
Both the patron and the warlock are presumably on some schedule with prices and fees all established right from the start - even the how's and why's for how this relationship could change is usually very clear. This is especially with demons and other 'chaotic' beings that cannot be trusted.
A DM may offer bonus features in any contract:
Even a celestial nobody that is trying to do the right thing to regain access to the Stairway To Heaven - one that brings their warlock cookies, milk and bedtime stories to their bed every night - will still be pitching their sale. They want their follower to do Goodie Two-Shoes stuff (help orphans, save the good king, steal from the corrupt, give to kind souls without hesitation and so on). They may also offer a first-level warlock multi-class to anyone who is willing to listen - especially to paladins and bards, those that understand lore and faith. A fiendish patron would listen extremely carefully to the needs of EVERYONE and offer underhanded temptation to anyone and anything willing to deal.
This last one is the one that is dearly missing in any campaign: making deals with any powerful being is a dangerous process: their motives are unfathomable and infinite. Even arch-angels see 'death' as a momentary awkwardness ('it isn't like their SOUL was harmed'), the End is justified by nearly any means and sacrifice is a daily necessity. Most angels are actually, according to literature, glorified hitmen. Fae will seek to twist contracts with an immortal and possibly selfish perspective. Fiends will go at great length to 'win' (sometimes even at their own expense). Those patrons from The Ultimate Beyond will have motives of no known design - their demands may not even be in a language you could recognize without magic.
You can see a patron as being a bit like the warlock's special thingy (be that a spell book, a familiar or a weapon) is similar to a sentient magic item with a special purpose. Although it does not command as much presence as a typical NPC, it plays behind the scenes, watching and waiting, always planning for their next chance to make things their kind of 'right'.