There are two kinds of modifications happening to units from Act Modifiers:
- Adding a unit to the lineup. This is the very first thing that happens. You are meant to treat it like the card had an additional rival unit printed to the lineup.
- Adding HP to rival units. This happens as the units deploy, per the wording in the rulebook: "On turn 1, rival deploys two units during its Deployment Step, adding 2 HP to each of these units." Also note, that this is an HP addition, not a Health stat addition. So nothing that multiplies Health stat would multiply this HP addition anyway.
There are only three Opportunities, currently, that need timing in place: Reckless, Confident, and The Brave Find Glory. Their timing occurs after all other modifications. You are meant to resolve all other modifiers, then you can decide if you want to use your Opportunity in this event.