At the beginning of every Fist of Guthix game, each player receives 300 catalytic runes along with 1,000 elemental runes. They can only be used to cast combat spells within the activity. While in Fist of Guthix, if you put a catalytic rune in the price checker, it says that each catalytic rune is worth 2 coins, even though you can never bring those runes out of Fist of Guthix to sell.
Due to a past update, Barbarian Assault now uses elemental and catalytic runes, instead of the standard ones. This is because players often find glitches that could let them escape Barbarian Assault with the runes.