Aldarc
Legend
I will be honest here and say that I am not sure. Ideally it would be something like the Goetic from Invisible Sun, which is my ideal warlock:That would be cool too. How do you think that would work mechanically?
However, I also recognize that this sort of playstyle is unfeasible for a game like 5e D&D, which utilizes more on-demand, instant gratification-based effects in the sense that spells just work. Stopping play for the warlock to do ritual summons and bargaining would be a no-go for legitimate gameplay reasons.How Goetics Use Magic
The first step to the Goetics’ summoning magic is figuring out what you want out of deal. Summoned beings can offer one of thirteen different things: counsel, non-combat aid, guarding you from danger, spying, the answer to a query, some kind of theft, assailing one’s enemies, restoring the Goetic’s health, influencing another’s mind, creating things, glorifying the Goetic’s appearance, binding the entity into an item, or serving as a long-term ally. This means that Goetics can have armor with bound-demon strength, furnaces where fire-spirit allies live, an angel friend they can call for advice, and many other tricks up their sleeve. You start off with the first four available, then at the second degree you gain access to the next three, another three at the third degree, and then finally glorify, binding, and ally at the fourth degree.
Next up you take precautions you want to set up (protective circles, having bribes on hand, etc), then you pay Sorcery cost for the entity you want to summon. If you want a demon-general that’s going to take a lot more juice than calling up a little fire-imp. You can also call up specific entities if you know their name, which requires a Sorcery check. If you are just calling for whoever might answer or the specific entity you want is fine with answering then your summoning automatically works.
Once they show up, though, that’s only part of the story. You still have to convince them to help and that takes one of four different approaches. If your argument seems like a good deal or the entity might be happy to do it then you can try persuading them. If you don’t think it’ll be an easy sell then you can try bribery with something the same level as the summoned creature. A bribe could be a magic item or treasure, something to consume, a favor in return, or even a mortal’s soul (a good bribe for a demon). On the other hand you might be feeling gutsy and try coercion to threaten the entity. Lastly, there’s the roleplayer’s tried-and-true approach of using trickery to make it seem like something the entity would want to do, talk them into a wager, or some other underhanded means.
If your approach works and the entity is persuaded, bribed, coerced, or tricked then they do the thing! If not, though… well entities aren’t always happy to be pulled away from their own business. Their exact response depends on the desires and nature of the entity, as well as how brazen and demanding you were in your failed attempt to win them over. Summoned entities could attack, establish an unwanted influence over the Goetic’s mind, or just escapes into the area they were summoned to causing untold chaos. Needless to say, none of these is a great option for the poor mage doing the summoning.
So what would it look like mechanically in 5e D&D? Again, I don't know. I think that part of the issue also involves the question of whether everything else stays the same. Are we adjusting the other spellcasters as well? Or do we want to mostly keep things the same for the sake of multiclassing harmonization? There are different ways to go, but it depends on a multitude of other factors.