EM is not Elemental damage bonus
Elemental Mastery affects reactions according to their own rules. It does not simply increase all Elemental damage. An Electro hit that triggers no reaction does not gain ordinary damage merely because its owner has more EM.
An effect may separately convert EM into damage or another stat. That is a kit or equipment rule, not an inherent property of EM. Read the conversion’s wording and conditions.
The benefit depends on the reaction
For Vaporize and Melt, EM improves the reaction bonus on the triggering hit. The underlying talent scaling still matters. For ordinary transformative damage, trigger level and EM are central inputs, while ordinary ATK and CRIT are not.
For Aggravate and Spread, EM helps determine the added damage. The resulting eligible hit can still benefit from damage bonuses and CRIT. Crystallize uses EM for shield absorption rather than ordinary attack damage.
Related reading: Understanding Elemental Reactions
Give the stat to the relevant owner
In an ordinary Hyperbloom setup, the Electro application that transforms the Dendro Core determines the trigger. The Hydro Character who helped create the Core does not automatically supply the Hyperbloom’s EM.
A reaction-focused build needs reliable ownership. If multiple abilities can trigger the reaction, inspect what actually happens before assigning all EM investment to one Character.
Related reading: Elemental Application & Auras
Equipment gives more than one effect
The Stringless has an EM secondary stat and a passive that increases Skill and Burst damage. Those are separate reasons it can suit an off-field attacker; the passive does not require every hit to trigger a reaction.
Replacing a scaling-stat sands with EM changes both the talent contribution and the reaction contribution. Evaluate the intended play pattern and available buffs. This guide establishes what to compare, not a universal EM target.
Related reading: The Stringless · Talent Scaling