Step 1: Break the keyword:
The word disguised means hidden. The word covert also means hidden. So the answer is likely a form with the word covert.
Step 2: Confirm with an example:
When a hero drinks a particular cold drink on screen as part of the scene, viewers see it as a story detail, but the brand is being advertised. This is covert advertising.
Step 3: Why merchandise differs:
Merchandise is a product with a logo, such as a mug with a show name. People know it is promotion. Nothing is hidden, so it is not the answer.
Step 4: Remove the others:
Informational ads are open and factual. Cross promotion is an open tie-up between two brands. Merchandise is the sale of branded items. None of these hide in entertainment.
Final Answer:
Option 2, covert advertising, is the form that hides the product in entertainment.
\[ \boxed{\text{Covert advertising}} \]