I agree that we have covered the bases in terms of abilities. We have 2 useful and complementary abilities already; any more, and this CAP will become too versatile, and the metagame won't be able to handle it. I, too, vouch for No Tertiary Ability.
This suggestion is actually the exact same effect as having 2 of the same type would be (Steel/Steel, Psychic/Psychic, etc.), something I advocated for way back in the typing phase. Next time, I would appreciate it if my potentially useful posts would not be deleted on the basis of a personal interpretation of forum rules.
However, if there must be another ability, I think it should be Moxie. It seems to me like the most different from what we have now, as well as equally compatible, risky and likely to be used. Moxie is definitely a close second choice for me as a tertiary ability.
A unique ability
I'm definitely not counting on this to win, but obviously it's still an option. My idea was to create "risky bulk" by introducing an ability doubles both its resistances and weaknesses, much like something out of the Pokemon TCG called "Allergy Panic". This could make bulky sets all the more feasible, as it would allow risk-taking strategies to have a place in sets outside of just trying to attack.
This suggestion is actually the exact same effect as having 2 of the same type would be (Steel/Steel, Psychic/Psychic, etc.), something I advocated for way back in the typing phase. Next time, I would appreciate it if my potentially useful posts would not be deleted on the basis of a personal interpretation of forum rules.