Alright so in Undertale you can dodge certain lasers even at point-blank range. Now sadly those lasers don't fit the requirements for being light speed but we can still calc how fast they appear to move in-game.
These lasers can move the entire length of the screen instantly. Here, the distance between the edge of the screen and the source of the laser is 419 pixels and Frisk themselves are 58 pixels high. 419/58 = 7.2241379310344828 the laser is about 7 times longer than Frisk is high.
Now according to this thing the average height for a 12 years old girl is 149.8 cm. Why 12 years old, why a girl? Because fuck you that's why. We don't know Frisk enough to have more precise statistics.
7.2241379310344828 x 149.8 = 1082.17586206896552344 cm.
Now this is all done in one frame, and Undertale runs at 30 FPS, meaning that this happens in 0.03333333333 seconds.
1082.17586206896552344 cm in 0.03333333333 seconds gives us 324.653 m/s, or mach 0,944606414. This is Transonic btw.
Since this is base, not in combat Frisk, it should essentially apply to everyone.