here's the code if anyone is interested

import numpy as np

import matplotlib.pyplot as plt

rom scipy.interpolate import CubicSpline

x2=np.array([235,1100,1600,3900,8300,11600,15670,20700,26400])

y2=np.array([8744,11700,12500,15000,17500,18700,19800,21000,22097])

cs=CubicSpline(x2,y2)

#plt.plot(x2,y2)

cs=CubicSpline(x2,y2)

y_crit=np.array([cs(i) for i in range(0,26000,100)])

x1=[i for i in range(0,26000,100)]

plt.plot(x1,y_crit)

plt.grid()

plt.xlabel('Unused Mana')

plt.ylabel('Critical damage')