Engineer

Models with this special rule may be deployed as part of one other friendly unit at the beginning of the game.

When rolling morale tests units may use the hero’s Quality value and when rolling to block use the Defense of the hero's unit until all non-hero models are killed.

Models with this special rule must accumulate X wounds before being removed as a casualty.

If a model with Tough joins a unit without it then you must remove regular models as casualties before starting to accumulate wounds on the model with Tough.

When a unit with multiple Tough models takes wounds you must accumulate them on a single model until it is killed before starting to accumulate them on another.