Amping Reactions

Melt and Vaporize.
AmplifyingReaction={2×(1+2.78×EM1400+EM+ReactionBonus)if, triggeringVaporize with Hydro orMelt with Pyro1.5×(1+2.78×EM1400+EM+ReactionBonus)if, triggeringVaporize with Pyro orMelt with Cryo1otherwiseAmplifyingReaction = \begin{cases} 2 \times (1 + \frac{2.78 \times EM}{1400 + EM} + ReactionBonus) & \text{if, } triggering\\ & Vaporize\ with\ Hydro\ or\\ & Melt\ with\ Pyro\\ 1.5 \times (1 + \frac{2.78 \times EM}{1400 + EM} + ReactionBonus) & \text{if, } triggering\\ &Vaporize\ with\ Pyro\ or\\ & Melt\ with\ Cryo\\ 1 & \text{otherwise} \end{cases}

Amping reactions scale on EM, reaction bonuses, and the damage of the attack triggering the reaction. Since they scale off of base damage, Amping reactions can make use of Crit/ATK stats of a character as opposed to just their EM and level. There are also reaction bonuses to further amplify this, which currently only exist in the form of the 4 Crimson Witch set and Mona's C1.

Melt

Melt is an elemental reaction triggered by applying Pyro onto a target already afflicted with Cryo or vice versa. Melt allows for a multiplier of damage amplification onto the attack triggering the reaction, heavily boosting the attack. Applying Cryo onto Pyro is colloquially referred to as a Reverse Melt as it has the smaller base multiplier of 1.5x as opposed to the 2x multiplier of Pyro onto Cryo.

Vaporize

Vaporize is an elemental reaction triggered by applying Hydro onto a target already afflicted with Pyro or vice versa. Vaporize allows for a multiplier of damage amplification onto the attack triggering the reaction, heavily boosting the attack. Applying Pyro onto Hydro is colloquially referred to as a Reverse Vape as it has the smaller base multiplier of 1.5x as opposed to the 2x multiplier of Hydro onto Pyro.