The demons of the Other Place can be summoned into the real-world from anywhere in the multiverse and at any time. Nathaniel needs time to summon his spirits and the more powerful and deadlier the spirit, the longer it needs to summon them. He uses the Amulet of Samarkand protects him from any magical backlash. All of his regular summons are considered by Das Jotunheimen as Agents but all of them have loyalty with Nathaniel and not his organisation.
His demons range from imps, foliots, djinni, admits and marids. The higher the ranking, the larger and more powerful it is. Every single classification of demon has to have some sort of form before entering real-world and most choose the being that fits them or whatever the situation calls for. But it's the amount of magic they have that makes sure that imps can't turn into skyscrapers. Only Marids can.
To summon a spirit, you must know it's true name. If you know it's true name, then they're basically your slaves. But if they know your true name, then you're on equal grounds with each other.
But these are not all of the classifications. There are lowly spirits who aren't even worth mentioning and then there are the great beings of such terrible power that only one (The Magician) magic-user that is alive can actually summon one without outright dying.
All of the classes from djinni and up can fire bolts of magical energy that blows shit up. Of course, the higher the demon is in the ranking, the more shit it gets to blow up. But that is only the basic power. Some control the elements, use fear to their advantage, shape shift into Giants to crush people, go invisible to the naked eye and etc. Ramuthra (the only greater spirit that The Magician can summon) is able to, as a Greater Spirit of the Other Place, warp the elements and change the physical state of whatever he comes in contact with. Due to his nature, he brought the chaos of the Other Place with him.
And before concluding, the less powerful, the longer they can stay in the real world without getting fatigued. I added this in so Nathaniel can't just wreck shit up with Ramuthra all the time. So imps can stay years while marids can only stay for around a week or two. Ramuthra can only stay for around an hour or two.
The following are some of his more notable summons, please note that excluding Ramuthra, they are almost constantly by Nathaniel's side whenever they can (if you notice, there are no imps or foliots in this list. They are that weak):
Bartimaeus of UrukThis demon has been with Nathaniel from the very beginning, when he went by the name John Mandrake and was an apprentice to middle-class magician. He is known by many names but most of the time his summoner just calls him Bart. The spirit is mostly known for his ingenious plans, cleverness, wit and smartass comments. In the
Guide to Demons and the Other Place, he is labelled "intelligent" but has "little to no power". The book has been claimed by some to be false (Bartimaeus in particular), so this may be completely inaccurate.
Bartimaeus is a mid-level djinni and when compared to other demons in Nathaniel's large cadre, he is a mere insect. But he is a valued strategist, a loyal summon and his best friend. But he is able to merge with his summoner at will, giving The Magician his abilities while also anchoring himself to the mortal world. He is known to also be a trap specialist but the traps tend to involve very comical ways in getting rid of someone. He takes the form of a lion because he said that "they were the only animals that were cool enough for him and be able to lug Nathaniel's ass around."
Duros the SandmanImagine Nathaniel's surprise when he found out that the Sandman was actually a spirit. Though he is nothing like the Sandman of the tales. Duros is a high-level djinni known for it's ability to make sand. He cannot manipulate sand, he can only make sand. Sounds pathetic but wait your mouth is filled with tiny pellets of sand while you laugh at his powers. He basically drowns people under sand to kill them. He has a very fierce temper and the youngest of his employ. He also has sadistic tendencies and scares most of the imps and lesser foliots it meets. He is known as the sandman for literally creating the Saharan desert so he could drown the humans below for ridiculing him for his powers. He doesn't respect anyone except for Nathaniel and basically hates everyone else.
Sonya the TerribleSonya is a high level afrit The Magician uses for his employ. Nathaniel learned her true name when flickering through his book of demons, waiting for his espresso in Neo-Starbucks. She caught his eye because of the kill-count the savage Sonya has gathered over her years fighting for humans. The demon claims she has killed ten thousand spirits in her career but some of The Magician's troublemakers say that 99% of that were messenger Imps. Though that number may be false, the demon's skill in controlling and manipulating fire speaks for itself. Her pyromaniac tendencies may be a problem but her gigantic, explosive, destructive balls of fire is pretty deadly. She is one of the Magician's more regular summons and her signature move of "Spam Fireballs till They All Die" makes her one of his deadliest. Other than her fireballs however, she is quite a glass cannon.
Jannilius the StrangeThis Marid is known for his calm behaviour, extensive knowledge of the Multiverse and his reliance on shape-shifting to kill things. Jannilius is an oddity among the demons because as a Marid, you should be an extremely angry, irritated spirit that hates being summoned. Instead, he has a very calm attitude which makes him the most valuable and powerful Marid of them all. A powerful being that doesn't hate your guts and is willing enough to not give you problems is hard to come by. The demon is extremely old and has been in the Other Place longer than most of the Greater Spirits. The reason he has so much knowledge about the universe is that he is actually a creation of Das Jotunheimen Scientists to test whether sleeper agents could be placed inside the Other Place. Unfortunately, the Marid was the only spirit created by the labs before it was blown up for unknown reasons. He defeats foes by shape shifting, his second favourite form being an Ultralisk.
Ramuthra the Most PowerfulOne of the most deadly demons recorded in magical history and the most arrogant, Ramuthra should not be taken lightly. Able to warp the physical state of those around him, control and create all of the elements and release such a large aura of hate and death that even afrits fall to their knees, he is
the most powerful spirit in Nathaniel's employ. He takes up so much of The Magician's power that he has to merge with Bartimaeus to even summon him quickly enough to even make him worth it in battle. There is a circle around him with a radius of ten meters that will transport any being in that circle into the abyss of the Other Place. Which, unless you're a spirit, means death. Equally deadly is his ability to turn solids into liquids or gas if you are at the most 30 meters away from him. His ability to manipulate and create all elements is quite scary. His only weakness is his arrogance. Against tougher beings (which is very few in number), he will be killed for his arrogance. He has a kind of respect for Nathaniel and that is the only reason why he is able to summon him without getting killed (aside from the Amulet of Samarkand of course).