I drive a 2002 WRX with Megan down pipes and cat removed. So I was out somewhere and my battery lost too much of it's charge to turn the starter. Luckily I was parked on an incline so I was able to pop the clutch to start it. I had to start it that way a couple of times before I could make it to the store to get a new battery/charge my battery. Right before that happened, I got a flashing check engine light that hasn't turned off for a few days. The car feels like it has reduced power because I think a cylinder is misfiring. I'm also thinking that I may have fouled a spark plug or two; after looking at my spark plugs on the driver side, they appear to be needing replacement soon. They were kinda dry and old looking.

What could be happening and what I should do to remedy? Any suggestions on applicable part replacements for this situation?