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I think regular poison should always be upgraded to toxic from poison-types and toxic from poison-types should become double toxic that skips the first round of toxic damage into the higher 2nd toxic damage round and continues on from there.
If there's a buff for damage from same-user-type moves then status effects should also be buffed somehow.
Paralysis from thunderwave from an electric-type should be 1-n-3 instead of 1-n-4 or you could reduce the effectiveness, like if fissure is used by a non-ground-type then it has a 1-n-4 chance instead of 1-n-3.
Also there should be a PP increase or decrease... heck, throw in power, accuracy, PP... everything should be affected slightly.
Gamefreak will never dig deep into the potential of their games.