We had a problem with the alchemist perfumer archetype, more specifically with his Effervescent Bombs (Su) and Healing Bomb Discovery.
How should it work?
Effervescent Bombs seem to be more of a special case than a Discovery, and it looks like it should heal in a square +5 foot radius each round with reduced values, but it's not clear how much.
Benefit: When the alchemist creates a bomb, he can choose to have it heal damage instead of dealing it. Creating a healing bomb requires the alchemist to expend an infused extract or potion containing a cure spell. A creature that takes a direct hit from a healing bomb is healed as if she had imbibed the infusion or potion used to create the bomb. Creatures in the splash radius are healed for the minimum amount of damage the cure spell is capable of healing. A healing bomb damages undead instead of healing them.
Effervescent Bombs (Su)
Rather than deal direct damage, a perfumer’s bombs create an effervescent puddle in a 5-foot radius for a number of rounds equal to the alchemist’s intelligence bonus (minimum 1). Each creature within this area takes 1d4 points of fire damage immediately and again each round it remains within or enters the puddle.
A creature caught in the puddle when it is first created can attempt a Reflex save (DC = 10 + half the perfumer’s level + the perfumer’s Intelligence modifier) for half damage. The effervescent bombs’ damage increases by 1d4 at 3rd level and every odd level thereafter. Effervescent bombs otherwise functions as bombs, and discoveries that apply to bombs apply to effervescent bombs.
I don't think the effects stack productively as written
Effervescent Bombs removes the direct hit damage in exchange for the puddle effect (and I personally find it ambiguous whether it also removes the normal splash damage). Healing Bombs removes both the regular direct hit and splash damage and puts in the healing effect based on the attached cure spell. Neither actually references how much damage the regular bomb would have done, even though the damage for Effervescent Bombs is calculated similarly. My interpretation of an Effervescent Healing Bomb as written is that it applies the healing bomb effect normally, and then also applies the effervescent bomb effect normally, resulting in a healed target standing in a pool of fire. Good for doing extra damage to undead, but not good for actual healing.
While I don't believe them to be rules-as-written, these feel like reasonable rulings to make as a GM:
Both effects attempt to replace the direct hit damage, so you can't have both active at the same time. Healing Bomb is not a valid discovery for the Perfumer archetype.
Treat the healing granted by healing bomb as positive energy 'damage', and apply the changes Effervescent Bombs applies to regular bomb damage (remove the flat bonus and reduce the die by one step) to the new 'damage' based on the cure spell used (so e.g. Cure Moderate will heal 2d6 per round)