There is at least one counter on a permanent you control except Xavier Sal.
Xavier Sal does not have summoning sickness.
Hyrax Tower Scout has no more than one +1/+1 counter on it.
Steps
Activate Xavier Sal's first ability by tapping it and removing a +1/+1 counter from Hyrax Tower Scout if it has one, or any counter from another permanent you control otherwise.
Xavier Sal triggers, causing it and all other creatures you control that share a creature type with it to get +2/+0 and gain undying until end of turn.
Resolve the Xavier Sal ability, causing you to populate.