So this came up the other day. We were fighting in Megalopolis, and Close Quarters Combat came up, making all damage Melee.
Our Ra player wanted to play the card that makes all Hero damage Fire.
We decided against it, but what trumps?
The most recently played card would take precedence, so everything would be converted to melee and then all hero damage would be conmerted to fire.
That's what we figured. We decided against it anyway, since we pulled out a tonne of damage & beat Plague Rat within the round.