Does Sandile's "Intimidating Fang" Ability also reduce damage done to Benched Pokemon?
Yes, it reduces all damage done by the opponent's Active Pokemon. Damage to your Defending Pokemon, your Benched Pokemon, and even damage done to your opponent's own Pokemon!
Source: Unbroken Bonds FAQ (2019-04-19), TPCi Rules Team (2019-05-02)

Relevant cards

Note: All applicable cards may not be listed below.
SM10_113
SM10_113