Add a Gravity-Variable in EntityLiving.class (called 'gravity' for example)

-> public double gravity = 0.08D; // default value of EntityLiving - Gravity

Replace in the Method "public void g(Vec3D vec3d)" of the EntityLiving the

variable "double d0 = 0.08D;" to "double d0 = this.gravity ;"

This will allow the possibility to change the gravity of an LivingEntity with a better solution then set Gravity to false and start a 1 tick loop to apply gravity manually.

A nice feature would be to auto save it as nbt so even a restart / chunk unload will not lose that gravity data.

Non-EntityLivings like Arrows, Items, Snowballs have custom Gravity values in each of their classes (EntityArrow=0.05000000074505806D, EntityItem=0.04D ....)