I'm starting to think that GameFreak might be using the Grass-Fire-Water and Dark-Psychic-Fighting triangles simultaneously at once for the new starters.
Jugding from their attacks in the trailer, it might seem that GF's hinting at a secondary typing for each, seeing that each pair of attacks are most likely of different types.
For Chespin, the 2nd attack might be Night Slash, and a Psychic-ish attack for Fennekin, and a pretty physical (probably Fighting type) move for Froakie.
So I'm guessing that GF might be downplaying the original type advantages that Chespin would have over Froakie, that Froakie would have over Fennekin, and that Fennekin would have over Chespin.
So in addition to these type advantages, if Chespin, Froakie and Fennekin are really Dark, Fighting and Psychic types at the same time respectively, then there would be no more type advantage. ie. Chespin's Dark typing would triumph over Fennekin's Psychic type even though Fire wins Grass.
Jugding from their attacks in the trailer, it might seem that GF's hinting at a secondary typing for each, seeing that each pair of attacks are most likely of different types.
For Chespin, the 2nd attack might be Night Slash, and a Psychic-ish attack for Fennekin, and a pretty physical (probably Fighting type) move for Froakie.
So I'm guessing that GF might be downplaying the original type advantages that Chespin would have over Froakie, that Froakie would have over Fennekin, and that Fennekin would have over Chespin.
So in addition to these type advantages, if Chespin, Froakie and Fennekin are really Dark, Fighting and Psychic types at the same time respectively, then there would be no more type advantage. ie. Chespin's Dark typing would triumph over Fennekin's Psychic type even though Fire wins Grass.