Some more testing from people more experienced with playing mods and terraria than I would be nice- but I decided to do my first "expert" difficulty run including spirit as the primary mod influence in my list and this glyph is uh...

Well it instant killed Atlas before he could do a single attack while being the primary damage output.

I like the idea, or what I believe the idea to be- proccing a status that stores your damage and then explodes- it's neat!
But during my playthrough it became a near immediate game breaker that made all encounters nearly instantly end- including the aforementioned Atlas and the moon lord himself.

I believe fully the glyph itself needs adjusted- but for fairness the "culmination" of effects causing it to instantly kill is the fact summoners can put it on their summons and sentries as well as their whip.

The actual output of my summons and sentries I'm using is already pretty good as they come from Storm's additions and their DPS is pretty decent as well as having nice ROFs to keep the damage coming.
The thing is my DPS jumps from 3-5k from my sentries alone up to 50k+ (ACTUAL NUMBERS FROM MY GOBLIN TECH) every time Null procs and it procs constantly when applied to all weapons in my rotation.

I have been doing a summoner playthrough, leaning on sentries, and the second I got Null and tested it against a dummy for a bit I thought "This might just outdo ruthless on my summons, I'll try it!" only for it to break all semblance of balance lol

Perhaps it shouldn't be capable of being applied to sentries/summons as having a ton of sources of Null damage going out means the enemy is always proc'd and always exploding and the explosions are FAR too large if the instant killing of multiple end-game bosses on expert is to be considered a metric.

This particular balance breaking interaction aside, been a fantastic time playing through this- Great stuff :)