Does Happiness affect anything in competitive battling?

Question

In Showdown!, I've never seen any Friendship perks happen. (toughing it out so you wouldn't feel sad, etc.) So does it affect anything other than Frustration/Return?

Answer 1

From XY to USUM, Friendship and Affection were two different mechanics. Affection was the one that allowed Pokemon to break through status or tough out hits, but it never allowed these benefits to take effect in online play or in battle facilities -- presumably due to their uncompetitive nature.

Starting in LGPE, Friendship and Affection were merged, but it will still never give the benefits in competitive play. The only in-battle things that Friendship affects are the base power of Frustration, Return, Pika Papow, and Veevee Volley.

Friendship (Bulbapedia)