The mobs took my pickaxe and chased me out of my mine.
I thought I should clear some sort of cave under my mine at level 29, there might have been a spawner or something. I mine a one-block window, and all hell breaks loose. Mini spiders are swarming out of the hole, creepers blow up a bigger opening, a throng of zombies surrounds me. I'm hacking at them, get poisoned with half health gone, so I wall myself off to drink milk and eat a small heart to heal as even more of them are coming out. My pickaxe somehow got lost in the middle of that. I mined my way around them with my hammer.
Take two, I'm still hoping to retrieve the pickaxe (it was a 18-speed boosted hepatizon), so I go back in with some punji sticks and sludge buckets. I placed punji sticks onto the stairs down, plopped some sludge a bit further so they can't come closer too fast. A major battle starts, I'm slowly pushing them back one block at a time, building dirt walls further and further into the cave (actually it must have been like 3 blocks into the actual cave, the rest must have been just my tunnels that I took back). Then something goes wrong again, a lightning creeper blows up the whole place, mobs are rushing in, I'm running away screaming (and burning). I lost all the ground I had previously gained and then some. I sealed all the branches, and won't be returning there ever again...