Cripple Level I needs to be purchased before Level II, and so on.
Players are limited in the level they can purchase by the level of their Rogue class - you must have Rogue 4 to purchase Cripple 4, for example.
Cripple is capped at 50% (for all levels). So, level 1 takes 10 tokens to get to 50% cripple (10+10+10+10+10), level 2 takes 8 tokens (15+15+15+15 [capped at 50]), level 3 takes 6 tokens (20+20+20 [capped at 50]), and level 4 takes 4 tokens (25+25 [capped at 50]). And all that work can be removed with 1 dispel token.
Cripple can be dispelled and, as such, one cleric token can be used to remove several tokens worth of work. It could however become useful when used by players that can't be dispelled, such as when stunning a player. Particularly warriors as a stunned warrior is still able to do significant damage. THIS IS THE PRIMARY USE (in the opinion of this contributor).