The ability of Wild Boar of the Sea is to damage all damaged enemies by 1, then it damages all enemies by 1.
The enemies don't die until the entire ability is completed.
This means if the opponent has a bunch of damaged units at 1 point, Wild Boar will kill all of them on the first pass and the second pass will result in excessive damage.
This means if you play Arnjolf leader into Wild Boar of the Sea, that's +3 of excessive damage on the Harpies spawned by Arnjolf and Bran will come down at a minimum of 11 points. Making Bran a really solid card with this leader.
I found this out accidentally. I was down a fair bit of points but figured I'd still play Bran, my final card. To my surprise, he came down at 18 points (aka +10 excessive damage) and I won.
Edit: If anyone is interested, this is the deck I was playing and I'm finding Bran + Harald to be a great pairing. It's not a great deck but it's fun. Discarding An Craite Warriors makes them a great target for War of Clans, 5 removal with a 4pt body.
Source: https://www.reddit.com/r/gwent/comments/tmng2a/psa_king_bran_has_a_great_interaction_with_wild/
