The most explosive engine card and the most commonly misused — deploy only into same-cycle value.
Karthus is best when at least one Deathknell can be triggered during the same action cycle.
Pilot noteStrong deployments: Karthus followed by Sacrifice; Karthus with an active Hook; before combat likely to kill a Deathknell unit; before the Beginning Phase with a controlled Dusk Rose death; before The Ruination; with multiple Temporary Reflections approaching death.
⚠ WarningWeak deployments: Karthus as the only unit; into open removal with no immediate Deathknell; when developing Vi or Fragmented would secure a point; when the only available Deathknell is the unit required to Hold.
Karthus and simultaneous deaths
Rules noteIf Karthus and other Deathknell units die simultaneously to The Ruination, Karthus still causes those other Deathknells to trigger an additional time. The game determines and queues the triggers while Karthus’s effect is still applicable, before the dead units fully leave the board. This is the foundation of the post-sideboard Ruination plan.◆src