Eating a Fragile Puffball when under the influence of (certain) other mushrooms seems to grant you energy of those mushrooms' effects equal to the amount of Energy gained from the Puffball.
Effects confirmed:
Altered State
Terrifying Introspection (probably means the other Introspections too)
Did not extend drought of breath for me, although that might be because it gave me more fae blessing instead, not sure if it can extend more then one thing.