Grass Knot & Low Kick are two rather unique attacks. They are unique in the manner that their base power is not contingent on the Pokémon using it, but rather on how heavy and bulky the target is. First lets just have a look at these two attacks

Name	Type	Cat.	PP	Att.	Acc.	Effect
Low Kick			20	--	100	A kick that inflicts more damage on heavier foes.
Grass Knot			20	--	100	Power increases if foe is heavy

These two seperate attacks incorporate the same functionality as eachother, but Low Kick is Physical while Grass Knot is Special. This factor requires you to completely factor in who you are using it against as well as the type.

Now, how is the base power calculated? There is a rather basic set up. It is based on your target's weight. This alone determines how strong, or how weak the attack is going to be. With as little as 20 Base Power, it can go as high as 120, making it a very powerful attack if used against the right team. Below is the set up of how it is calculated

Weight	Base Power
Under 10kg Under 22lbs	20
10.1kg - 25kg 22.1lbs - 55lbs	40
25.1kg - 50kg 55.1lbs - 110lbs	60
50.1kg - 100kg 110.1lbs - 220lbs	80
100.1kg - 200kg 220.1lbs - 440lbs	100
Over 200kg Over 440lbs	120

Now that table may not seem very helpful to you, well click on the headers and you will get a list of the Pokémon that are inflicted with that specific damage through the use of Grass Knot or Low Kick. A very handy thing