Snape grass

Snape grass can be obtained when Fishing manta rays, this requires a fishing level of 85. Snape grass will automatically appear in your inventory. It is only used as an ingredient to make Prayer and Fishing potions by using the Herblore skill.
There are also a couple of Monsters from which you can obtain snape grass.

Prayer potions are created by using the snape grass on an Unfinished ranarr potion. This requires a herblore level of 35 and will grant 440 experience.
Fishing potions are created by using the snape grass on an Unfinished avantoe potion. This requires a herblore level of 56 and will grant 565 experience.

Monsters that drop Snape grass

Monster	Combat level	Quantity	Rarity
Aquanite	114	1 - 4
Dagannoth mother	100	2
Dagannoth mother	100	7
Dagannoth prime	303	4
Dagannoth rex	303	4
Dagannoth supreme	303	4
Dagannoth	74	2
Dagannoth	92	1 - 2
Dagannoth	92	5 - 6
Glacor	475	5 - 9
Gorak	145/149	1
Werewolf	88	1