Theka the Martyr

Scarab courtyard
Separate Theka from the scarab clusters before starting broad area attacks. Remove his plague and change damage schools when he transforms; do not drag the fight through the rest of the courtyard while physical attacks are ineffective.

Theka the Martyr
Elite UndeadTheka's transformation stops Physical and Shadow damage while Fevered Plague and surrounding scarabs can keep the courtyard fight dangerous.
Abilities

Fevered Plague
Interrupt Fevered Plague when possible and cure the Disease when it lands.

Theka Transform
Use damage other than Physical or Shadow while the transformation is active; otherwise deal with engaged scarabs and wait for the immunity to end.
Tank- Separate Theka from untouched scarab clusters before the group uses area damage. Hold the courtyard position through his transformation and collect scarabs already attacking the healer rather than dragging Theka across more beetles.
Healer- Remove Fevered Plague as a Disease. Keep healing the courtyard pull during the transformation even if physical attackers have stopped damaging Theka.
Damage- Change to a damage school other than Physical or Shadow during Theka Transform. If your attacks cannot hurt him, finish engaged scarabs without sweeping area damage across untouched clusters.