1) Yesterday you told me that "at" was possible in the sentence "He raised his sword and gave a mighty blow at the beast". Are you sure you can't use it? Are both "He gave the beast a mighty blow" and "he gave a mighty blow to the beast" possible? Thank you very much for your help.

2) Can you say "which of the two prepositions is better in this context (and not is best"?)
3) How can you express this: "Students can have two excuse notes for each term" (if they are not prepared and don't want to be tested orally)
4)The student was reprimanded by the teacher for forging his father's signature (?)
5) The clock smashed through the windscreen and I had to have it replaced.

1. Are both "He gave the beast a mighty blow" and "he gave a mighty blow to the beast" possible? Yes, either one works.

2. You need to use "better" because you're comparing two things, not three or more (which would be when you'd use "best").

3. Try this: Students can have only two excuse notes during each term.

4. and 5. I don't know what you think the problems are in these sentences.