Summoning fiends is risky business.
They do not have your best interest at hand and will betray you at first chance.
Still there is a process to summoning them safely and if you are successful, they can
help in battle, or running errands.
The Wizard class is what you’ll want if you wish to summon fiends from the lower planes.
Although warlocks and clerics have some power there as well.
But, wizardy is the most robust of the classes when it comes to controlling and summoning
fiends.
There are three types of fiends, Devils, Demons, and Yugoloths.
Each comes from a different lower plane, The Nine Hells, The Abyss, and Hades respectively.
Devils and Demons hate one another, constantly fighting in the blood war that’s been raging
for what seems like forever.
Any experienced spellcaster can summon one of these creatures using the spells Summon
Demon, or Infernal Calling.
But that is too dangerous, a free willed devil or demon running about ready to attack the
conjurer isn’t helpful.
For example if you do summon a demon it makes a Charisma saving throw at the end of each
of its turns to shake off your control.
Potentially useful but we’ll want to exert more control over our summoned fiends.
You’ll want to bind the creature to your will, ensure it follows orders.
True names can help in controlling a fiend.
Everything in the multiverse has a true name, except perhaps the gods themselves.
Knowing a creatures true name gives you power over it.
In the case of fiends it aids in summoning the correct one, and gives disadvantage on
it’s spell check to break free from your control.
Learning true names is an arduous process.
You must perform research consulting libraries and sages all across faerun, especially if
you’re searching for a particular fiend.
Spells like Legend Lore can assist the wizard in this process but it usually requires 2d12
months to discover a true name.
However if the DM wishes it an entire campaign arc could be spent discovering the true name
of a fiend.
The useful thing about true names is you’ll be summoning the same devil or demon each
time, and not one at random.
Let’s start with devils.
Their lawful nature makes them a bit easier to control.
But don’t be fooled they will manipulate the situation towards an evil end if there
is a sliver of possibility.
You’ll need to utilize the 5th level spell Infernal Calling which requires a ruby worth
at least 999 gold pieces.
The casting takes a minute and summons a devil within range.
Each of your turns after summoning this creature you can attempt to issue verbal commands to
it, the devil will comply if it’s something the devil would do naturally, or a command
that would bring you the caster closer to evil.
Otherwise you need to make a Charisma skill check contested by the devils Wisdom.
You make the check with advantage if you know the devil's true name.
Succeed and the devil will carry out your instructions until it completes the activity.
Demons are slightly different, more chaotic and can’t necessarily be reasoned with using
persuasion checks like a devil can.
You must exercise your force of will over the creature.
The spells Summon Lesser Demon or Summon Greater Demon will bring you a creature from the Abyss
to the prime material plane.
This demon will initially listen to you and do what you request, but each round it makes
a Charisma saving throw and if it breaks free of your control be wary.
The demon is chaotic and will attack the nearest non-demons to the best of its ability.
Removing concentration on the spell the demon disappears back to the Abyss after 1d6 rounds.
If you know the demon's true name is has disadvantage on the Charismas saving throw versus your
spell save DC.
If you want a more constant companion there is always the Warlock Pact of the Chain route,
which provides you an imp familiar to watch over your on your adventures.
If you desire a stronger ally there is a process to bind a larger fiend into your service.
First create an inverted magic circle to summon a demon into.
This will keep them from attacking you while you cast other spells on the creature.
The creature can’t willingly leave the circle, and won’t be able to attack you.
You’ll want to upcast this so the circle lasts longer than an hour because our next
spell takes one hour to cast.
Planar Binding can bring the demon under your control for 24 hours.
Once under your control you’ll need to request the demon create a demonic amulet for you.
A demon that stores part of its essence in an amulet can avoid being destroyed if killed
in the Abyss.
But anyone who holds such an item can command the demon to do as they wish.
With such an item you can command the demon to do exactly what you want, while it remains
on the prime material plane.
The item doesn’t have to be an amulet, it must simply be bound into an object.
Perhaps a gem, ring, or even weapon would be more suited to you.
Devil Talisman’s also exist but these are ancient relics inscribed with the true name
of the devil it controls.
They were bathed in the blood of worthy sacrifices, and are quite evil relics.
The knowledge of creating this might lie with the devil himself, and using the same planar
binding method you may be able to convince a devil to tell you the process.
If you obtain a devil talisman you have control over a particular devil.
Finally if you want a more constant demonic companion you’ll need to summon your fiend
using their true name, the demonic amulet or devil talisman, and the gate spell.
Other lower level spells like Summon Demon or Infernal Calling only keep the fiend for
a limited amount of time.
Using the gate spell you conjure a portal and using the true name can pull your fiend
into the prime material and they’ll reside with you permanently until killed.
Upon which they return to their home plane and await to be summoned again.
Remember these artifacts that aid you in controlling your fiend are evil.
They can cause terrible nightmares and influence your behavior.
Don’t be surprised if your alignment starts to shift towards evil or chaotic the more
you wear them.
Don’t get possessed by your demon, and remember they are magically bound to you but that doesn’t
mean they won’t kill you if given a chance.