It's hard to say for sure. Arceus is super powerful as the creator Pokemon. But the Creation Trio also has some really strong abilities. So it could go either way depending on how the fanfic is written.
In fanfics, the battle between the Pokemon Creation Trio (Dialga, Palkia, Giratina) and Arceus can be really intense. Usually, Arceus is seen as the god - like Pokemon, but the Creation Trio also has incredible powers. Dialga controls time, Palkia controls space and Giratina rules over the distortion world. Their clash might be about power struggle or some sort of cosmic balance. It really depends on how the fanfic author wants to portray it.
One possible plotline could be that the Lake Trio discovers a threat to the world that Arceus is either unaware of or is causing (unintentionally perhaps). So they have to battle Arceus to stop this threat. Another could be that a powerful villain manipulates the Lake Trio into believing that Arceus is a danger and they must fight it.
In a fanfic, it really depends on how the writer wants to portray it. If the writer wants to emphasize the unique abilities of the Lake Trio and perhaps give them some sort of combined power boost, they could potentially defeat Arceus. However, Arceus has the advantage of being a creator - like figure in the Pokemon world. It has the ability to create and shape the world, which gives it a very high level of power. So, generally speaking, Arceus is more likely to be the victor, but in the world of fanfiction, anything can happen.
The members of the Pokemon Creation Trio can vary depending on the fanfiction. However, common ones might include Dialga, representing time; Palkia, representing space; and Giratina, representing anti - matter or the distortion world.
In a Pokemon Arceus Wish Fanfic, the plot could center around a character who is in desperate need of something. For example, a region might be facing a great danger like an evil team with powerful Pokemon. The protagonist then makes a wish to Arceus for the strength or the means to stop this threat. This could lead to an adventure where the character has to prove themselves worthy of the wish being granted. Arceus might set tasks or challenges for the character to complete before fulfilling the wish.
One idea could be exploring the origin of the Creation Trio's powers. Maybe they got their powers from an ancient and mysterious Pokemon or a powerful energy source in the Pokemon world. Another idea is to have them face a new, powerful enemy that threatens the balance of the Pokemon universe, and they have to combine their unique abilities to defeat it.
A storyline might involve a group of trainers who are all affected by a strange phenomenon in the Pokemon world. They come together and decide to make a collective wish to Arceus for a solution. Arceus could then give them a quest that requires them to cooperate and use their unique skills and the powers of their Pokemon. As they progress through the quest, they discover the root cause of the phenomenon and are able to resolve it, thanks to Arceus' guidance.
In a fanfic, Ash might have a chance against Arceus. Ash has proven time and again that he can adapt to different situations. He could potentially find a Pokémon's weakness or use some unorthodox strategy. However, Arceus is the creator of the Pokémon world. It has the ability to manipulate reality on a fundamental level. So, on paper, Arceus should win. But fanfics often play with the rules, so Ash could win through some plot - driven miracle.
A fanfic centered around the Pokemon Lake Trio in the Hall of Origins might involve a young trainer's journey. The trainer, curious about the legends of the Lake Trio, embarks on a quest to find the Hall of Origins. Once there, they discover that Uxie's knowledge is not easily accessible, Mesprit's emotions are overwhelming, and Azelf's protection is hard to bypass. But through determination and respect for the Pokemon, the trainer gradually uncovers the secrets of the Hall and forms a special bond with the Lake Trio.