pi guy cryptic 12

"Decided to finally set a proper large cryptic, rotational symmetry and all. This puzzle is also a pangram, meaning that every letter appears at least once. Recently discovered that this was a common feature of some well-established cryptic crossword publications, so I thought I'd have a go. This can also be an extra solving aid; if you haven't used a Q or Z yet, you know you'll have to eventually."