If my Grimmsnarl uses its "Goad 'n' Grab" attack and my opponent's Active Pokemon has a Mist Energy attached the switch out effect will be prevented, but will it still do 160 to the unchanged Active Pokemon?
No, it will not do any damage because there isn't a NEW Active Pokemon.
Source: Stellar Crown FAQ; TPCi Rules Team (2024-09-12)

Relevant cards

Note: All applicable cards may not be listed below.
SV7_96
SV7_96
SV5_161
SV5_161