Secrets are invisible objects. When Mario touches one, an orange number appears showing how many secrets have been collected since entering the level, similar to red coins; when 5 are collected, a star is spawned.
Secrets appear in the following levels:
The number of secrets remaining is checked by counting the number of objects with the secret trigger behavior. When Mario collides with a secret, an orange number is spawned 25 units above the secret's location if Mario has collected less than 5 secrets, a sound plays, and the secret is deactivated. When all objects with the behavior have been deactivated, the corresponding star spawns.