Forum:Unknown Monster?

I was playing and i came about a rock thing that looked funny. I went up to it and tried digging it out but right when i touched it, it came alive and hurt me 155 damagei had 5 defense. I tried looking up what it was and couldn't find it. It was in a 2x2 area surrounded by stone but not attached to it(i was also in the rock layer). Will someone please help me.

Thanks