What is the plot?

I can't provide a factually reliable beat-by-beat spoiler for that episode from the information available here.

What is verifiable is that the 2024 STAYC YouTube entry "[STAY:SEE⁉] #??? 이 영상은 이제 제 겁니다 제 마음대로 이야기 할 수 있는 겁니다🤫" was published on 2024-01-11 and is listed as episode #77 in STAYC's 2024 video lineup, but the available source snippet does not include the episode's actual scene-by-scene content.

If a summary or transcript of the episode is provided, a complete chronological spoiler can be reconstructed from it.

What is the ending?

I can't reliably give a factual ending summary for that specific STAYC episode from the information available here. The only verifiable detail gathered is the episode title itself, which is listed as a STAY:SEE video from January 11, 2024.

If a transcript, full video description, or a trusted recap is provided, I can turn it into the short ending and the scene-by-scene expanded narrative you want.

Is there a post-credit scene?

No post-credit scene is identified in the available sources for this episode, and the search results do not provide an episode transcript or recap confirming one.

The only source directly tied to STAYC in the results is the group's Wikipedia page, which notes Stay:See as behind-the-scenes content, but it does not mention this specific episode or any post-credit segment.

If you want, I can also help verify whether the episode has: - a mid-credits scene, - an end card/cutaway after the credits, - or a post-episode bonus clip in the YouTube upload.

Which STAYC members are featured most prominently in [STAY:SEE⁉] #??? 이 영상은 이제 제 겁니다 제 마음대로 이야기 할 수 있는 겁니다🤫?

The available source identifies the episode title and release, but it does not provide a full scene-by-scene breakdown or cast focus list for this specific video.

What is the exact premise or setup of this STAYC [STAY:SEE⁉] episode?

The source only confirms the episode title and that it is a 2024 STAY:SEE release; it does not supply enough detail to describe the premise precisely.

What happens in the opening moments of [STAY:SEE⁉] #??? 이 영상은 이제 제 겁니다 제 마음대로 이야기 할 수 있는 겁니다🤫?

The available information does not describe the opening scene, so a precise answer about the first moments cannot be verified from the gathered source.

Which member says or reacts to the line about the video being theirs and speaking freely in this episode?

The source preserves the Korean title phrase, but it does not identify which member delivers it or how the line is used in the episode.

What specific behind-the-scenes activity or setting is shown in this STAYC episode?

The source does not include a detailed description of the episode's setting or activities, so the specific behind-the-scenes content cannot be confirmed here.

Is this family friendly?

Probably yes: it appears to be an idol behind-the-scenes style episode rather than anything explicitly mature, so it should be generally family friendly for most viewers. A few moments may still be mildly upsetting or objectionable for very sensitive children, such as loud shouting, startled reactions, exaggerated teasing, tense competitive energy, or brief emotionally intense conversations.