Simple question, if you're a mythic heirophant and are a cleric with the Animal Domain does the mythic ability affect your animal companion (+4 to companion's effective level) and does it increase your companion's effective druid level above your character level? (-3 +4 = net+1) and would this stack with boon companion for a +4 total effective druid level?
1. Yes, but most GMs will impose the perceived design-intended limit of your effective druid level being no higher than your character level. Without that inference, you would indeed treat your effective druid level as being one higher than your actual cleric level.
2. Boon companion stacks, but it also has an explicit cap at your character level, so it wouldn't be any help to you unless you take a lot of non-cleric levels.
1. Yes, but most GMs will impose the perceived design-intended limit of your effective druid level being no higher than your character level. Without that inference, you would indeed treat your effective druid level as being one higher than your actual cleric level.
2. Boon companion stacks, but it also has an explicit cap at your character level, so it wouldn't be any help to you unless you take a lot of non-cleric levels.
OK makes sense.
Does the feat Boon Companion apply first (bringing your effective Druid level up to your HD) and then the Mythic Domain add an additional +4 on top of that?
I suppose it's moot if the game goes up to level 20 (like wrath of the righteous) unless your GM lets you bring the Animal Companions effective level into epic levels through house rules using the pattern established by the animal companion progression graph
I don't know if there's a specific rule for it, but I've always seen it played that manipulating the order in which passive feats/abilities are processed to circumvent restrictions is a non-starter. YMMV, though! Especially since we're talking mythic here--having an extra-beefy companion is peanuts compared to what you can do with stuff like wild arcana, mythic vital strike, or divine source.