It would be two coronets that are linked like the Yin and Yang rings.
One allone does nothing, but when two towers each wear one of the coronets,
they swap all of their bonus values.
The transfer is not perfect and in the process the bonus is reduced and the resulting bonus
is about 50% of the source bonus.
One could use it to transfer from Mr. Iron to another card.
Normaly I would wait to the last moment but with challenges the cards maybe would be used earlier.
It's a cool idea, but everything must be swapped, otherwise you could just add the attack of a tower to another one with an amazing effect. You could even get rid of the penalty.
It could be a pretty cool thing to see. Great one buddy! +1 for me.