When Geralf's Mindcrusher dies, its undying ability and Goldberry trigger.
Resolve the Geralf's Mindcrusher trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
When Geralf's Mindcrusher enters the battlefield, it and Intruder Alarm triggers.
Resolve the Geralf's Mindcrusher trigger, causing a player to mill five cards.
Resolve the Intruder Alarm trigger, untapping all creatures.
Holding priority, activate Goldberry's first ability by tapping it, moving the +1/+1 counter from Geralf's Mindcrusher onto Goldberry.
Resolve the Goldberry trigger from step 2, untapping it.
Activate Goldberry's second ability by paying ({U} magic symbol) and tapping it, moving the +1/+1 counter from Goldberry onto any permanent except Geralf's Mindcrusher, and causing you to draw a card.