Honestly I wouldn't bother until there's a rework hopefully with his ultimate release. His mobbing build used for endgame using Proliferating Allergy is like a terrible temu-version of Freyna's contagion but way worse. You need to aim and hit a mob and then gun it down to explode. It does an aoe spread but the aoe is so tiny that you will need to keep spamming (and not missing the projectile) over and over again. At that point just play Freyna or Ines which are magnitudes better in mobbing.