Inquisitor 1375

[Ripper]

I've solved all the clues, but unfortunately only found some of the misprints, so I'm completely in the dark what to do with the letter (I assume the same one) do I just put one large one or lots of elongated ones?
Any help withe the misprints would be very helpful.
Thanks in advance

[roslyn251254]

there are 4 letters which are special and make a "large" word in the grid.
Then you have to highlight the more usual version elsewhere in the grid.
7 letter word hint on next to bottom row of grid

[maurice]

There are 3 different letters composing a 4-letter word, which has to be entered once in the normal way but forming a square, the second time also forming a square but each letter written large over 4 "cells". The whole you can only understand when you have the theme, which is a natural illusion.
Try to get the last word in the 4-word phrase,the first letter of which is the correction to the clue 10d.That same word also emerges if you have solved all the clues in the middle of the penultimate line in the grid. Sorry that all sounds so complicated, but I feel I can't give any more away!

[Ripper]

Thank you roslyn251254 & maurice, I'll have another go!

[maurice]

Good luck! Let us know when you get stuck again (but not too quickly)!