As a DM, sometimes I watch the encounters I set in motion with a bit of foreboding, like "this could go badly..."
Watching 2 carrion crawlers almost take out a party with 4th level fighters and clerics... was a tense moment for everyone! Fortunately, the first level halfling fighter saved the day!
My carrion crawlers are like facehuggers, but with 8 tentacles, a maw plus legs and a 9 ft long body.