One could argue that Merlin from Arthurian legends is the most powerful sorcerer in fiction. He has the ability to see the future, transform shapes, and use powerful magic to aid King Arthur. His magic is often portrayed as being very ancient and mysterious.
Powerful spells are a key factor. A sorcerer like Doctor Strange in the Marvel universe can cast extremely complex and powerful spells. He can open portals to different dimensions and use magic to manipulate time, which gives him a high level of power compared to other fictional sorcerers.
One popular fanfiction idea could be Harry Potter unlocking a hidden ancient magic that makes him even more powerful than in the original series. He could use this power to quickly defeat Voldemort and then go on to reshape the wizarding world, for example, by introducing new spells and magical teachings.
One of the most powerful characters in fiction is Superman. He has super strength, can fly, has heat vision and is nearly invulnerable. He can move planets and survive in space, which makes him extremely powerful in the fictional world.
Some of the most powerful fictional beings are the Q Continuum from 'Star Trek'. The Q are omnipotent and can manipulate time, space, and reality at will. In the world of Japanese anime, Goku from 'Dragon Ball Z' is also very powerful. His power levels keep increasing throughout the series and he can perform incredible feats of strength and energy projection. Another is Lucifer Morningstar from the 'Sandman' series. He is an extremely powerful fallen angel with a vast array of powers.
One of the most powerful items in fiction is the One Ring from 'The Lord of the Rings'. It has the power to corrupt those who possess it and gives its bearer great influence over others. Another is the Elder Wand in the 'Harry Potter' series. It is considered the most powerful wand, able to perform magic with great strength. And the Infinity Stones in the Marvel Cinematic Universe are also extremely powerful. Each stone controls an essential aspect of the universe, and when combined, they give the wielder god - like powers.
A popular powerful dragon in fiction is Toothless from 'How to Train Your Dragon'. Despite his small size compared to some others, he has the ability to shoot plasma blasts, is extremely fast and agile, and has a very close bond with Hiccup which gives him an edge in battles.
In the 'Dragon Ball' series, Zeno is an extremely powerful being. He can destroy entire universes with just a thought. He is the king of all the universes in the Dragon Ball multiverse. His power level is so high that no other character can really compare to him in terms of sheer destructive capacity. And his decisions are absolute, which shows his dominant position in the Dragon Ball fictional world.
One of the most powerful vampires in fiction is Dracula. He has superhuman strength, the ability to transform into various forms like a bat or wolf, and can control the minds of others. His immortality also gives him an edge, having lived for centuries and accumulated a vast amount of knowledge and power over time.
The Infinity Gauntlet in the Marvel Universe is extremely powerful. With all six Infinity Stones inserted, it gives the wielder the power to do almost anything. Thanos uses it to snap his fingers and wipe out half of all life in the universe with a single thought. It can manipulate time, space, reality, power, the mind, and the soul, making it a weapon of near - unlimited capabilities.