I've been hearing rumours about tampering with abilities and now it seems the possibility of a legitimate No Guard + Fissure combo is in jeopardy. Anyone know for certain?
This isn't tampering with Abilities, this is totally "legal."
Come January, virtual console Red/Blue/Yellow will be PokéBank compatible with Sun and Moon. In Gen I, Machamp can learn Fissure via HM. When transferred to Sun/Moon, the Gen I Pokémon will be given the abilities they gained in later games. Machamp's is No Guard. Hence why it may be possible to get a No Guard Fissure Machamp.