Sam Riegel wrote this

Or Freddie Wong

I know you’re joking, but

Natural regeneration, devoid of magic, requires more calories than the severed limb will provide. The ring of regeneration creates new flesh via magic, bypassing the rules of physics

I see this as an excellent strategy to use with inexperienced players.

Let the gamify the tactics a little, give them a false sense of security and then BOOM give them a genuinely intelligent opponent that makes them pee their pants

Oooh, or you could bring in another player to play the enemy similar to this greentext (tl;dr: FelixLaVulpe tells the story of playing a minotaur against an min/max adventuring party at the DM’s request. Spoiler, it goes very poorly for the overconfident party)

Sometimes the players just forget to open the door. I was doing a one-shot with a friend, playing SW5e. He had opened a couple doors already, but this time he approaches and says:

Player: “I ring the doorbell”

GM: “You are met with silence. Nothing happens”

…

Player: “Helper droid, help me get this door open”

GM: “The droid approaches the door. He slowly turns his head and you feel his photoreceptors bore into your eyes. He extends a digit and, while maintaining eye contact, slowly presses the door open button. The door opens with a pneumatic burst. ‘I am happy to problem solve for you, Master. Is there anything else you need me to do? Turn on a light, perhaps? Make stim tea? I do enjoy extending myself behind my core programming as an assassin.’”

Player: “‘Shut up and guard the door.’ I step inside the room, what do I see”

GM: “As you cross the threshold, two automated turrets drop from their enclosures in the ceiling. Surprise round, roll for initiative”

It was a fun game. For me