Best Offence is an achievement that requires the player to defeat the Kalphite King after triggering his immortality and then defeating him again.
One way to trigger Kalphite King's immortality ability by using the ultimate ability Frenzy when he is below 35k hp during his melee phase.
To get the Immortality to activate, you need to use 'unload' to kill the Kalphite King whilst he is in his corresponding form (Ranged)
For melee this is Frenzy, for mage this is Smoke Tendrils.
- The achievement name is a reference to the saying "The best defence is a good offence", encouraging proactive attacks in order to hinder an enemy's ability to effectively launch their own offence.