Overview
She is the storm that is approaching! Px4 comes through with her Neural Upgrade. An already popular HG albeit one who had fallen off in the meta with time, Px4 MOD does come with a pretty specific but potentially strong niche.
Px4’s new Skill 2, Motivating Bonus, applies a new status effect called ‘Fragility’ to all non-boss enemies as long as you meet the requirements. When enemies with this status take a critical hit, they take another instance of damage that’s equal to 3% of their remaining HP and goes straight through HP Shields, which can be strong. She also gives a very small teamwide damage bonus every time the team collectively scores 100 critical hits.
So what’s the catch? It’s those aforementioned requirements. Skill 2 only works when there are only at most 2 different Doll types on the field, which severely hinders her team building capabilities if you want to make use of it. Standard RFHG teams can work with this skill, but if you require any of the strong defensive Dolls (Suomi MOD, DP-12 MOD, etc), Px4 will be the first to become useless. In most general situations where Px4’s Skill 2 is applicable, you would likely have been able to clear the fight with just a regular RFHG in the first place, though Px4’s Skill will likely help kill them a bit faster. There’s also the issue of her Skill 1 conflicting with her Skill 2 as it decreases the team’s Crit Rate, but this can be offset by bringing other HGs that buff Crit Rate back up or simply disabling her Skill.
When her conditions are fulfilled, Px4 can be a valuable asset to the team. Even then, she still works as a general buffer unit too. Her restrictions sadly make her not a complete slam dunk answer to all your problems, but she can be useful to have and can perform well in the right situations. MOD2 is her most important upgrade, with MOD3 being totally unnecessary as her SPEQ is not important.
It should also be noted that going all-in on synergy with Px4’s Skill 2 is not recommended for general content. While her Skill can be quite strong against the right enemies, you should not go out of your way to raise more niche dolls for the sole purpose of synergy. Doing so may help you kill things a little bit faster compared to less-specialized echelons, but will not meaningfully change the outcome in most fights and will still become useless the moment enemies start fighting back, due to the restrictions applied. Ranking is another story of its own.