Hello Alexander! For the second part of this sentence, to get the meaning of it, I think we should focus on the whole term "maintain his invincible front" instead of cutting the verb out. [emoji]Here're some ideas that might be helpful: 1.The word "front" can mean the outward appearence of a person, the way you want to show yourself to others. [emoji]Eg."That smile is just a front—I don't think she actually likes me at all." [emoji]Eg."Don't front!---Don't act like a badass when you're not!" The first example is from Merriam-Webster Distionary and the second one is from Urban Dictionary. Not like these two, the sentence you post is apparently using "front" in a positive way. So, I would say "He always maintains an invincible front" is just a fancy way of simply saying "He's invincible". Let me end my speaking with another example from TED[emoji]: "I was 28, and like so many of us when we are in good health, I felt like I was invincible." I'm open to new ideas;) Have a nice day!

In this case, it means the boy tries to put on a look that shows he is not afraid of anything (maybe a scowl or a confident look). Sometimes you may see someone "put on a brave front" (i.e. tries to look brave)- I guess they are similar. There is no mention what the person is feeling though (could be feeling very scared as well), so you could interpret the word "front" as the image of the person they are trying to project, and not their true feelings.