The "naturemonevo" is looking likely to be a dipplin evo. The trailer seems to hint we'll be facing off against Kieran in the BB league, maybe as champion, and he has a dipplin in Teal Mask. Plus, Khu tweeted in a reply that he went and caught two new shiny applin for his shiny dex in prep for the DLC.
In addition to the number of new mons riddle, Khu also may have hinted at the number of forms:
6 + 1 + x for the twitterless. (That +x is what Khu wrote, nothing to do with Twitter's rebranding)
Notably, Teal Mask had 6... two of which it seems are going to be taken up by Sinistcha/Poltchageist unless it really happens to be standalone. Since we know Terapagos has a form, that would seem to use up the only slot for Indigo Disk, which would mean that if Blood/Harvest moon Ursaluna is a form it would be in Teal Mask. That leaves only 3 slots. If Ogrepon has a form, then it would seem to preclude the loyal three getting any forms because only 2 slots would be left, so potentially Ogrepon gets multiple forms. If Poltchageist is standalone, then it looks like there's enough room for Ogrepon + the loyal three to each get a form. Or, since the balloon mini-game had 4 types of Ogre, maybe Ogrepon just gets 4 forms...
To summarize:
If Sinistcha exists, the Teal Mask forms would seem to be:
-Sinistcha
-Poltchageist
-Ursaluna
-Ogrepon x 3
If Poltchageist is standalone, then we could have
-Poltchageist
-Ursaluna
-Ogrepon
-Loyal 3
or
-Poltchageist
-Ursaluna
-Ogrepon x 4