Creature Paralysis generally hits in a Flat Range Reduction. For example the Mummy paralysis range might reduce your speed from between 100 - 240 speed points. The effect is also not cumulative, so the next Paralysis they cast might hit you for less or more and your speed will adjust accordingly.
Example
Characters Base Speed - 320
Mummy casts Paralyze of 180
320 - 180 = 140 (Character Base Speed - Paralysis Value)
Characters Speed - 140
Next Round
Character Speed - 140
Mummy casts Paralyze of 120
320 -120 = 200 (Character Base Speed - Paralysis Value)
Characters Speed - 200
Source