Ok we create a empty ENTITY struct with pointer ENTITY* door_ent;

We create a action call door()

We assign that action to 3 of any of the entity types (model, sprite, map_ent).

Each of these 3 get a automatically assigned a entity struct, and each get a memory pointer. Each are created one at a time.

Each of the 3 is then assigned into the empty pointer struct door_ent=my;
thous - only that last create entity actual shares a memory pointer address with door_ent.