Unlock the nest after Bigfoot
The two paths near Fire Ant Hill lead to the same boss room. Both need the Iron Sword, obtained after Bigfoot. This optional encounter has 60 base HP and rewards Investor plus Alternate Reality.
Guard the lifesteal, not just the big combo
Poison Pierce thrusts the proboscis into its target, steals 8 HP and applies Poison. A missed guard both hurts you and restores the boss, so this is the important single-hit cue to learn. Double Pierce loops vertically twice, stabbing at the bottom of each loop for 8 piercing damage per hit.
Handle the summoned swarm
Call for Help adds a Mosquito Swarm when there is space. Clear it if its extra attacks are forcing more recovery than your party can afford; otherwise finish a nearly defeated boss. This is a target tradeoff, not evidence of a separate Demo 5 blood-drain phase.