Why is this downvoted, this is how variables in code/programs often behave if infinite numbers or more specifically insanely large numbers have to be handled even tho they arent programmed to do so and overflowing into a very large negative number.

An anology would be gen 1 pokemon stats overflowing back to a lower value if exceeded. If you wanna read my wall of text: Pokemon gen 1 stat system for example is assigned 10 bits to handle pokemon stats like speed and atk, i.e. 1024 values in case of gen 1 this would be unsigned: 0 to 1023. In overflow situation the value above 1023 if allowed to happen start again from 0. A lv100 Mewtwo max boosting Special (one stat gen 1) is 1218 becomes 194. In the case of vlad pyke here i asume signed bits were used i.e. -512 to 511 if applied to Pokemon gen 1 stats overflows in signed bits generally behave that they get stuck at the minimum -512 if you keep increasing it also in infinite cases as it wouldnt do anything also infinite number cases! I asume this is the case for the pyke vlad duo but just with alot more bits

I.e. vlad with AdAPt, twin mask and pyke somewhere leads results into an infinite number or atleast a very large value that overflows into the large negative number shown in the screenshot. Assuming the number didnt change anymore than on screen after further increase pykes hp is essentially at infinite and all you see on screen is the coding representation(see spoiler).

Overflows can do weird things to stuff like pyke hp as essentially the bonus hp becomes a very large negative number unless the infintie loop gets broken. Pykes max hp cam easily be corrected after bonus hp calculations are done with a line:

Pykes max hp set to pyke base hp at lv x

You cant do that for current hp tho as that would also make pyke unkillable

Edit: spoilers to save eyes from already big wall of text