Does a Pokemon with multiple types such as Scovillain with the "Double Type" Ability count for two different types of Pokemon for Toxtricity's "Loud Mix" attack?
Yes, Loud Mix checks for the number of types of Pokemon on your Bench, not how many Pokemon there are.
Source: Obsidian Flames FAQ Addendum; TPCi Rules Team (2023-08-10)

Relevant cards

Note: All applicable cards may not be listed below.
SV3_25
SV3_25
SV3_72
SV3_72