What does “stay + adjective” mean?

Is there any difference in using "old man" and using "father"? Why did he use "old man" instead of "father"?

That's a great question. The term "old man" is kind of endearing here. Most people don't just say "old man", it's usually "MY old man", as Chris Pratt does in the clip. Also, "old" in this context may not even be referring to age. It can also mean long-standing, and calling your dad "old man" means that you've spent a lot of time together with him. That's why we have other similar phrases such as "old buddy", old pal" and "old friend". Ex: Oh, my old man and I have a great relationship. Ex: Yes, she's an old friend from school.

What's it mean? Is it same as saying "what you doing?"

Yeah, that's right! the term "up to" can mean "doing something." So the phrase "whatcha up to?" or "what are you up to?" means "what are you doing?" Ex: What are you up to tonight? = What are you doing tonight? Ex: Whatcha get up to last weekend? = What did you do last weekend?

What is different between saying "try to be more descriptive" and "try being more descriptive"?

These two sentences are very similar. Both are perfectly acceptable to use and both have the same meaning. The only difference between them is the form of the verb "to be" along with the tense of the sentence. "Try to be more descriptive," the verb is in its base form and the sentence is in the present simple tense. "Try being more descriptive," the verb is in the present participle form and the sentence is in the present continuous tense. Here are some examples of sentences with these phrases being used. Ex: Could you please try to be more descriptive? Ex: Try being more descriptive, please.

Can I use "completed" instead of "accomplished"?

Good question. "Accomplished" can be used as a synonym of "completed" and vice versa. As verbs there is however subtle nuance between them. "Accomplished" means to finish something successfully, "completed" on the other hand simply means to finish or reach the end of something. Because of this they can't always be used as synonyms of each other. In the case of this clip, "mission accomplished" means that they finished successfully. Changing it to "mission completed" means they finished the mission but doesn't necessarily mean it was successful. Ex: I completed my homework. (Finished but I don't know if it is successful until my homework is marked) Ex: I will complete my novel tomorrow. (Finish) Ex: He was very accomplished in his work. (He was successful) Ex: Did you accomplish everything you needed to? (Complete)

I'm always confused between "sympathize" and "empathize", can I use "empathize" here? And does he mean that he pities her?

They differ slightly! To "sympathize" is when you understand something from your own perspective. To "empathize" means to understand from the other person's point of view and not just from your understanding or experience. The idea of "sympathy" can be a way of pitying someone. However, here, the pity comes more in the "but sentiment?" part since he himself enjoys "the distraction of the game." He pities the "sentiment" part of her. Ex: Oh, I sympathize with you, those history classes were so long and boring at school. Ex: I won't ever know what that feels like, but I empathize with you! Can I do anything to help or support you?