Found a rather large bug where Boomerang Step's attack speed was set to 690ms instead of 900ms, which has been persistent for all iterations. Not sure how it happened but it's fixed for the OP, and whenever I feel like updating GMS version it'll be fixed there too.
Some more information after playing:
Each hit of Meso Explosion counts as an attack, and raises Critical Growing/Prima Critical's count by one. While training, I can bring my critical rate from 32% to 100% with two Meso Explosions.
There appears to be either a cap on how much this can occur on a single target, or there is a hidden cap on the actual damage done by Meso Explosion. It also very often lands on 100%. It only reliably passes it and resets if I'm already in the 90s. The most I've ever seen from a single target is about +30%, which is coincidentally 15 hits. There may be a 15 hit cap on Meso Explosion on a single target in this case, I'll need to either find something with extremely high HP and see if I can get the expected damage, or find something with Weapon Cancel and see if there's only a cap on critical gain. It may also be a product of lag though.
An interesting and unrelated aspect of Critical Growing/Prima Critical is if you're at 100% critical rate you miss any hits, it won't reset. This includes when attacking more than one monster, so if you're training at a high level area, you can use Meso Explosion to raise your crit rate to 100%, and then spam Savage Blow/Muspelheim at 100% critical rate. If you hit 8 monsters with Savage Blow, and even one line misses, you keep your 100% Critical Rate.
I'm going to attempt to work an algorithm and see if it's possible to use Meso Explosion purely for keeping your critical rate high, since it's obviously detrimental if it's used at high critical rates compared to Boomerang Step, Sudden Raid, Assassinate (if it can critical yet), or even Edge Carnival. i.e. if you use Meso Explosion at 100% critical, the first hit (or maybe the first few hits?) will be 100%, but the rest will be reset to whatever your base is, and gain from there, whereas if you are at 100% with Boomerang Step, both hits of Boomerang Step's massive 742% will be criticals.
Some more information after playing:
Each hit of Meso Explosion counts as an attack, and raises Critical Growing/Prima Critical's count by one. While training, I can bring my critical rate from 32% to 100% with two Meso Explosions.
There appears to be either a cap on how much this can occur on a single target, or there is a hidden cap on the actual damage done by Meso Explosion. It also very often lands on 100%. It only reliably passes it and resets if I'm already in the 90s. The most I've ever seen from a single target is about +30%, which is coincidentally 15 hits. There may be a 15 hit cap on Meso Explosion on a single target in this case, I'll need to either find something with extremely high HP and see if I can get the expected damage, or find something with Weapon Cancel and see if there's only a cap on critical gain. It may also be a product of lag though.
An interesting and unrelated aspect of Critical Growing/Prima Critical is if you're at 100% critical rate you miss any hits, it won't reset. This includes when attacking more than one monster, so if you're training at a high level area, you can use Meso Explosion to raise your crit rate to 100%, and then spam Savage Blow/Muspelheim at 100% critical rate. If you hit 8 monsters with Savage Blow, and even one line misses, you keep your 100% Critical Rate.
I'm going to attempt to work an algorithm and see if it's possible to use Meso Explosion purely for keeping your critical rate high, since it's obviously detrimental if it's used at high critical rates compared to Boomerang Step, Sudden Raid, Assassinate (if it can critical yet), or even Edge Carnival. i.e. if you use Meso Explosion at 100% critical, the first hit (or maybe the first few hits?) will be 100%, but the rest will be reset to whatever your base is, and gain from there, whereas if you are at 100% with Boomerang Step, both hits of Boomerang Step's massive 742% will be criticals.