You can set an alert to trigger only when maximum X number of metrics are in an anomaly. To do it, go to alert settings, click on additional conditions, and choose Maximum Metrics in an Anomaly from the drop-down menu:
Example Use Case
A company monitors a group of metrics, but the NOC team is interested in being alerted only when one or two anomalies are evident. The case in which many / most of the metrics are simultaneously anomalous is considered as not interesting (e.g., can be dismissed as a system glitch).