You control at least one creature token with base power 2 or less.
Xavier Sal does not have summoning sickness.
There is a removable counter on a permanent you control.
Steps
Activate Xavier Sal by tapping it and removing a counter from a permanent you control, creating a copy of a creature token you control with base power 2 or less.
When the creature token enters the battlefield, Intruder Alarm and Serra Redeemer trigger.
Resolve the Intruder Alarm trigger, untapping all creatures.
Resolve the Serra Redeemer trigger, putting two +1/+1 counters on the creature token.