Espero que esto te sirva....

1- en el PBS pokemon busca el poke que quieres que no se pueda capturar, en el listado de los diferentes atributos, en rareness pones un valor entre 0 y 3 y el pokemon sera casi imposible de atrapar.

2- puedes poner una condicional que algo no pase asta que se cumpla el script, por ejemplo que el pike te corte el paso, y asta que no se cumpla la batalla no deje de hacerlo.

Edito:
Para evitar que sea posible escapar seria algo asi:

pbWildBattle(PBSpecies::KECLEON,20,10,false)

Acá Todo explicado pero en inglés:



To generate a wild Pokémon battle, call pbWildBattle(X,Y,V,C) where:
•X is the species number of the Pokémon.
•Y is the Pokémon's level.
•V is optional and represents the number of a variable to store the result of the battle (for example, if V is 2, then the result of the battle -- 1=won; 2=lost; 3=escaped; 4=caught -- will be stored in variable number 2).
•C is optional and is true if the player can escape from the battle (the default is true).

The following code example starts a battle against a Kecleon at level 20, and stores the result of the battle in variable number 10.
pbWildBattle(PBSpecies::KECLEON,20,10)

To change the kinds of wild Pokémon found in an area, you can use the "Set Encounters" option in the Pokémon Essentials Editor (editor.exe). After doing so, it is enough to put grass tiles (or other tiles with terrain tag 2) on the map for wild Pokémon to appear there -- no events are necessary. Pokemon Essentials supports two different encounter types: Land and Cave. For Land encounter types, wild Pokémon will appear only on the grass. For Cave encounter types, wild Pokémon will appear anywhere. Several other encounter types are also supported.






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