Basically, if main series Pokémon games treated Abilities the same way as the PMD series does, by giving every Pokémon access to all the Abilities they can have at the same time. Just a few things, though;
1: Hidden Abilities are counted in this as well. All Arbok would have Intimidate, Shed Skin, and Unnerve all at once.
2: Form-exclusive Abilities remain form-exclusive. Red-Striped Basculin would have Adaptability, Reckless, and Mold Breaker, but not Rock Head- only Blue-Striped Basculin would have that.
3: When Mega Evolution occurs, the Pokémon gains its Mega Evolution's Ability on top of the ones it had prior to Mega Evolving- Mega Pinsir, for instance, would have Aerialate, Mold Breaker, Hyper Cutter, and Moxie.
4: Skill Swap would switch all of the user's Abilities with all of the target's Abilities. Entrainment would replace all of the target's Abilities with all of the user's Abilities, and Role Play would do the opposite.
5: Trace would only overwrite Trace with the opponent's Abilities, leaving the Pokémon's other Abilities intact. A Porygon switching in on a Quilladin would end up with Download, Analytic, Overgrow, and Bulletproof.
Alright, now, how would this affect things? What becomes broken? What becomes useless? What doesn't really change much?
Hmmm: Mega Kangaskhan with Scrappy and Parental Bond Mega Garchomp with Sand Veil and Sand Force Breloom with Technician.Effect Spore and Poison Heal Porygon-Z with Analytic and Download Cincinno with Technician and Skill Link Mega Heracross with Moxie and Skill Link Mega Gyarados with Mold Breaker and Moxie Lugia with Multiscale and Pressure Mega Lucario with Justified and Adaptability Mega Gengar with Levitate and Shadow Tag
And so on...
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