When an Immobilised model declares a Melee, Run, Charge, Scenario, Stand Up, Heal, or any action including movement (including changing facing before the action), the model must make a Size (6) Challenge test.
If unsuccessful the model’s action is considered resolved.
If successful the model removes all Immobilised markers and resolves its action as normal.

An Immobilised model cannot declare the use of Special Attacks or Defences.
A model can declare a Wait Action to remove all Immobilised markers.
Enemy models in BtB with an Immobilised model can declare actions as if they were not in BtB.
If any other effect moves an Immobilised model, then remove all Immobilised markers from it.

Intangible models have Immune [Immobilised].