でしょう roughly means "don't you agree" or "I agree", I didn't play the FF games so I don't have enough context to translate its original meaning here.
手に入る literally translates to "put into hand", but it means "acquire" in the context of opening a chest and finding a potion. Japanese games say "potion put into hand" and English translations say "You received a potion".
全く literally means "truly" or "very" but a lot of the time people use to mean "seriously" in a sarcastic sense. Like, "seriously!?" or "jeeze!". A beginner would think "very" but somebody with experience would know they're just complaining in a way that doesn't elicit* a response.