Yeah, it's a teigu. Esdeath called it a dog once and the children were surprised to hear.
But for some reason they did not notice... Or perhaps it was applied too quickly for them to react?
Anyway, you're going against manga facts now, that clearly point out that the poison takes effect before it's noticable.
Either way, if Serioux gets poisoned killing her is easy. Koro would have to defend her in order to keep her alive, and come on... Firing nukes when she's paralyzed? She can't even aim...
As for the titan form, Stylish obviously knows about the nukes, meaning it won't be in vain. This time he's able to eat more minions than just 3, meaning the titan would be bigger. Add the fact that there are still minions and poison on the battlefield, this means that:
a. Serioux has to hide in Koro in order to traverse the battlefield, meaning she can't nuke him.
b. Serioux gets exposed to the poison, or blown up, or both.
Even moreso, he can squish her rather easily, as he was even able to knock Susano'o away, who so far has better agility feats than Serioux.
You must be registered for see images
Are you sure Serioux will be able to deal with all these enemies at once? And have you also considered just how much distance Stylish can traverse during the exchange? And what happens if he goes full titan from the start?
The odds are definitely in Stylish's favor.
