found a bug, dunno what happened though
my first rat had a heal and the second had a parry (slot 2), once i used these, a lizard that was supposed to be parried killed me (the gray one targeting the top rat)
death screenshot:
It looks like there are enemies surrounding both rats. Both of the items in slot 2 are instant use, so you would heal on the first screen and prime the parry on the second, and then the enemies would attack on both screens. the right screen enemies would be parried but the left screen enemies would attack as normal and deal damage (and because there are two of them, you would take more damage than you healed)