Thanks again for your reply, you're really helping me out here!
I only just realised that you can have multiple conditions for a single event thanks to you, so that's a huge help.
The crouching works fine now! As does the crawling! There's a few problems so far though, the biggest being that I can't seem to be able to get back up once I'm down... probly another stupidly easy to solve situation, but here's my event sheet:
Sorry if it's a little confusing (I didn't think ahead here), but the boldened Crawl, and the Crawl in quotations are a variable and an animation, respectively (Something I'll change later, for sure).
26 = Enter crouch mode
27 = Exit crouch mode (back to Idle)
28 = Crawl when in crouch mode
29 = Exit Crawl mode (back to crouch)
30 = Can't jump when in crouch mode
EDIT: I've managed to get it working the way I want it. Again, thanks to JudgementXD for all the help!