Greater Explosive Magic

General Feat (Prerequisite: Explosive Magic Origin Feat, the ability to cast spells, Level 4+)

Ability Score Increase. Increase one ability score of your choice by 1, to a maximum of 20.

Explosive Spells: Choose one of the following improvements for your explosive magic -cantrip: it gains a bonus to damage equal to your spell ability modifier (if you don't already apply it otherwise), or it deals half damage on a successful saving throw.
In addition, choose one school of magic that includes spells that deal damage. Whenever you cast a spell of 1st level or higher of that school and roll the maximum value on a number of damage dice equal to or greater than the spell’s level, you can roll one additional damage die from that spell and add the result to the damage.

Chain Casting: Whenever you cast a spell of 1st level or higher from the chosen school and roll a number of 1s on its damage dice equal to or greater than the spell’s level, you can expend your Reaction to cast a follow-up spell without expending a spell slot. The follow-up spell must deal damage and must target at least one of the targets of the original spell. It can be a cantrip, a 1st-level spell if the original spell was 3rd level or higher, or a spell of 2nd level or lower if the original spell was 6th level or higher. The follow-up spell cannot trigger Explosive Spell.