The Guardian is no longer triggered by tadpole usage, instead it is triggered by reaching a certain cutscene location;
the cutscene of the party being overwhelmed by the Absolute's voice and the artifact being used to shield themselves from it. It's triggered by either approaching the Goblin Camp bridge, the Mountain Road bridge or the Broken Road Pass.
Once you reach any of these three locations the Guardian will appear the very next long rest. Personally I really like that it's tied to progression rather than long rest/tadpole spamming.
