I want to make an event that makes it so that the player can see every pokemon in the pokedex. Is there a simple script command that makes it so that all pokemon are owned? If not, is there one that gives the player every pokemon?
When you see a Pokémon, you also record its form and mark that as seen too. This allows it to be viewed in the Forms page of the Pokédex. In your case, you would want every form to be available. The Debug option "Fill boxes" does this; here's the code it uses (slightly tweaked for your purposes):
$Trainer.formseen= if !$Trainer.formseen
$Trainer.formlastseen= if !$Trainer.formlastseen
for i in 1..PBSpecies.maxValue
$Trainer.formlastseen[i]= if !$Trainer.formlastseen[i]
$Trainer.formlastseen[i]=[0,0] if $Trainer.formlastseen[i]==
for j in 0..27