Law staff

The Law staff is a magic weapon, released with the Dungeoneering update, on 12 April 2010. It costs 60,000 Dungeoneering tokens. Players can store up to 1000 Law runes within it, and when used it has a 1/10 chance of not using a law rune.

As a weapon, it is tied as strongest staff available in f2p with the Nature Staff. The Gravite Staff has a stronger magic attack bonus.

Cost Analysis
The following is a comparison of the cost per cast of spells using Law runes while using an elemental staff as opposed to using a Law staff. The cost per cast when using the Law staff is approximate and assumes that exactly 1 out of 10 Law runes are saved.