Went over all Pokémon I pronounce wrong for gens 1-3:
- Psyduck. Correctly pronounced with a silent P, like similar words (e.g. psychic, psychiatrist, psychology, pterodactyl, pneumonia, etc.), but since English isn’t my native language, I always pronounce both those words and this Pokémon including the P, so psy-duck.
(Even though I do correctly pronounce other silent letters in other Pokémon names, like the W in Poliwrath or Y in Gyarados. 
) - Growlithe. I always pronounce it as grau-light due to that trailing E, instead of grau-lith.
- Ariados. For some reason, I still keep pronouncing the A’s for this Pokémon as I’d do with Dutch words: àh-ri-àh-dos instead of ai-ria-dos (‘ai’ like in the word air), even though I don’t do that (anymore) for the majority of other Pokémon names, like its pre-evolved form Spinarak ironically enough.
- Wobbuffet. Despite the double B, I always pronounce it as Wó-buf-fet (like the second O in the word domino) instead of wohb-buf-fet.
- Breloom. I pronounce it as brea-loom (like the ‘brea’ in the word break), as apposed to breh-loom (like the ‘bre’ in the word umbrella).
- Slaking. Again pronouncing it like the Dutch A, because I see the Dutch word ‘sla’ (lettuce in English). So I pronounce it as sláh-king instead of slay-king.
- Nincada. Also a Dutch A. Although this one is a bit harder to explain, since the official prouncation already uses two different sounds for the two A’s. The correct pronunciation is nin-kah-duh (where the ‘kah’ is similar as the “hard A” in father). But the Dutch pronunciation would be nin-ká-dá (where both the ‘ká’ and ‘dá’ doesn’t really have good English examples.. I guess kinda like you might say ‘kaaah’ and ‘daaah’, perhaps.. Anyway, you can listen to how I pronounce it at the left here (ignore the right section).)
- Mawile. I’ve always pronounced it as mah-will instead of mah-while. Kinda like Marill, but with a W instead of R.
Not sure why I’ve always pronounced it like that tbh. Only just now it occurred to me that it’s wrong, haha. - Aron. Since Aron is a normal Dutch name, I always pronounce it like that: aah-ron, instead of ay-ron. (Lairon I do pronounce correct however, and I only now realize Aron and Lairon are pronounced exactly the same, except for the added L-prefix.
) - Vibrava. I pronounce it as vee-brava (like ‘vee’ in Eevee) instead of vy-brava (like the Y in sky - or, you know, the I in vibrate
). - Whiscash. I pronounce it as wish-cash instead of wis-cash (like ‘wis’ in wisdom).
Funny to see that basically all the gen 1 Pokémon I’ve previously mispronounced in a similar thread back in March I currently pronounce correctly. So I guess once I realize they’re wrong, I correct them in my head over time. 
And forgot about this one for a moment, haha:
Greetz,
Quuador