They could only make a single summon at first because of lack of experience and it had to be something that was weak minded and wouldn't be able to resist however overtime they managed to create an army of summons. They could teleport to any summon teleport, any summon to their side could share power with as many summons as they wanted. They had used sheer overwhelming power to create a room in which time affected differently.
A thousand years inside was an hour outside. When they left 4 years had passed by on Earth. The individual remained at the age of 16 years old due to how powerful the healing liquid and healing stones were; they slowed down the individual's ageing drastically. The individual had mastered all of their powers and their stamina was almost limitless and it's recovery rate was insanely quick the consumption of energy stamina was at the very minimum. They were a master of everything they gained that day. They also gained an ability that would allow them to combine two individual summons into a single entity that was superior to the individuals as the strengths of one summon would amplify the new summon the weaknesses of the individual summon would be covered by the combined resistances so if one was immune to cold while the other was weak against cold the new entity would be immune to cold and it was like this for every weakness and if they both had the same strength or resistance than the new entity would have the combined strength or combined resistance of the two everything was affected the new entity would no longer be the same as the two individuals but would be its own personality and existence this was still only new so the individual could only fuse two together.