Splashing is the act of purposely wearing items with bonuses that total at least -65 Magic attack (e.g. full plate armour with d'hide vambraces, or full plate armour and a Cursed Goblin Staff), and attacking a weak opponent that cannot be interacted with by other players (such as any NPC that can be pickpocketed, or rats, which can be killed by cats). Simply bring enough runes, and turn auto cast and Auto Retaliate on.