File:Special Duration Up Vulnerability Chart.png

Formula
$$B = \% Change = (0.99 * A - (0.09 * A)^2 ) / 30$$

Killer Wail normally leaves the player vulnerable for 120 frames, and Inkstrike for 100 frames as of 2.7.0.. 60 of these frames are affected by Special Duration Up.

$$C = Killer Wail Vulnerability Time (frames) = 60 + 60 * (1 - B)$$

$$D = Inkstrike Vulnerability Time (frames) = 40 + 60 * (1 - B)$$

$$Killer Wail Vulnerability Time (seconds) = C / 60$$

$$Inkstrike Vulnerability Time (seconds) = D / 60$$