
Gauss |

It is not multiclassing.
Example:
Class X Archetype 1 substitutes/changes powers 2 3 and 6.
Class X Archetype 2 substitutes/changes powers 1 4 and 5.
Advancement is as per class X but powers 1 2 3 4 5 and 6 are all different due to the two archetypes.
There is no multiclassing archetypes from the same class.
- Gauss
Edit: added clarification.