Soul ForgeATK, double attack rate, critical hit rate, debuff resistance, and hostility are boosted / DMG taken is lowered (Can't be removed) grants him many powerful buffs, but consumes 100% charge bar to activate.
Draws attacks towards himself via Hostility Up to defend more vulnerable allies.
Powerful Enmity-based nuke is strengthened further through his charge attack buff.
Gamewith's recommended EMP build for Vaseraga (Earth).
Priorities
Prioritize Critical (★3×2) first, followed by DEF (★2×2), Water DMG Down (★2), and Hostility UP (★1×2). As Soul ForgeATK, double attack rate, critical hit rate, debuff resistance, and hostility are boosted / DMG taken is lowered (Can't be removed) gives him 100% DA, DA is a low priority for him. Enmity also is a low priority, as while he will be taking most of the hits, his high durability will make it difficult to cut his HP down low enough to benefit from it.