Go memory of felwinter artifact for bubble bros. I did them all on my Titan at the start of TTK because once u do one on a character u get to skip the first half of the quest on the other swords. It was tedious but not terrible. If you're being conscious about ability kills when collecting the planetary materials, u should be alright. Then go to the dark beyond door or the siege of the warming thrall parade for any remaining ability kills. For gunslingers, do kills count on enemies caught in the blast with the golden gun kills explode targets perk? Either of those mission would be great if they do.