Resistance Effect

Resistance is a Minecraft effect that can make you take less damage.

Resistance 128
Resistance 128 (also known as resistance 127).

As the Minecraft wiki states, the damage reduction for it is calculated like this:

100% - (20% * level).

In case of resistance 128, the damage reduction is:

100% - 20% * 128 = 100% - 2560% = -2460%

This is also the reason why the negative damage of instant damage 28 and 29 is able to damage you. See the [inexistent wither/poison page] for more info on the ways to protect yourself against this (in most cases)