It's hard to say. Ash has a lot of experience and a strong bond with his Pokémon. But Tobias also has very powerful Pokémon. It could go either way depending on how the story is written.
Well, it could be that Tobias has some evil plan to take over the Pokémon world and Ash stands up to him. Maybe Tobias has captured a bunch of rare and powerful Pokémon, and Ash, with his Pikachu and other friends, battles him to free those Pokémon and stop his tyranny.
Well, in this 'ash fights tobias with lugia fanfiction', if it follows the normal Pokémon battle rules in the anime. Ash has to carefully plan his moves with Lugia. Tobias might have some really strong and rare Pokémon. Lugia's advantage could be its large move pool and high stats. Ash would need to read Tobias' moves and react accordingly. For example, if Tobias sends out a fire - type Pokémon, Ash could use Lugia's water - based attacks or its ability to create strong winds to put out the fire and gain the upper hand.
In a fanfiction where Ash fights Tobias, Ash might win by using his bond with his Pokémon. He has a deep connection with his team which could give him an edge. For example, Pikachu might unleash a super - powerful Thunderbolt at a crucial moment.
The plot might start with Ash somehow obtaining Lugia for the battle against Tobias. Then, the battle could be a back - and - forth exchange of powerful moves. Ash would be trying to outwit Tobias, who may have some unexpected Pokémon up his sleeve. Maybe in the middle of the battle, Lugia gets injured and Ash has to come up with a new strategy on the fly to keep fighting.
In the 'ash's charizard vs tobias' fanfiction, the outcome often depends on how the author wants to portray Ash's growth. If the author wants to show Ash as a more developed trainer, Charizard might win through some clever tactics Ash has taught it. However, if Tobias is depicted as a really formidable opponent, it could be a very close call or even end with Tobias' victory, which would then lead to Ash's determination to train harder.
I'm not sure of a specific 'ash defeats tobias fanfiction' off - hand. You could try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just type in the keywords 'ash defeats tobias' in their search bars, and you might find some great stories.
I think Tobias would be a very difficult opponent for Ash. However, Ash has shown time and time again that he can adapt to any situation. He might notice some weakness in Tobias' strategy or Pokémon that others have missed. His ability to form strong bonds with his Pokémon could also give them an extra boost in battle. So, in the end, Ash might just come out on top.
There's also 'Ash and Tobias: A Rivalry Reborn'. In this fanfiction, Tobias resurfaces after a long time, and his new and improved Pokémon team challenges Ash in a series of intense battles. It delves deep into their rivalry and how both have grown since their last encounter.