- A transformable frame has two modes.
- A transformable frame can only transform during its turn.
- It has to have a Transformer System. When that system is destroyed the frame is locked into its current mode.
- A transformable frame has a different system loadout in each of its modes, while still having a maximum of four systems.
- A transformable frame cannot have more than two systems and the Transformer system in each mode.
Technically a transforming frame can have five systems but, since it has no more than three in any one mode, I think we can handwave that away.
How's that for a start?