10 Worst Non-Signature Abilities In Pokémon Games
7. Solar Power
Of all of the weather-based abilities, Solar Power is the worst.
In intense sunlight, a Pokémon with Solar Power will have an increased Special Attack stat, but it will also lose 1/8th of its HP after every turn. It's the only weather-based ability that both relies upon and suffers under a certain type of weather. Yes, Dry Skin also causes HP loss in sunlight, but at least it restores HP in rain. Solar Power, however, does not. It is harmed by the very sunlight that it craves.
While this ability is rather uncommon with only nine Pokémon getting access to it, it is unfortunately what Houndoom ends up with upon Mega-evolving. Literally, all of its possible abilities as a normal Houndoom (Early Bird, Flash Fire, and Unnerve) are better than Solar Power, so it makes using Mega Houndoom a questionable decision at best.
Also, as an unrelated aside - Mega evolution is a stupid game mechanic and should never have been added to the franchise. Moving on -