Withers' Door - A puzzle

The door is magically locked and can only be opened with a passphrase. 

There is no keyhole, no lock, no visible hinges and no mechanical trap. There is a brass doorknob of a lion's head that does not turn, but is hand sized and positioned to easily grasp to push open. There is a large "W" letter-form, also in brass, sitting proudly above the dark wood.  Orange candlelight can be seen to shimmer under the door from the other side, which catches the edge of a well-used WELCOME mat sitting squarely in front. 

If Detect Magic is cast, the door, the knob and the W do all shimmer with evocation magic.

If the players verbally say anything directed towards the door, and they're not holding on to the lion head brass knob... psyche them out with a dramatic pause, to make them think they've done something wrong... and reveal "nothing happens". Even saying the correct passphrase without holding onto the door knob results in the passphrase not being "heard". 

When a word/s are spoken toward the door and the speaker is not holding onto the lion head brass knob, its eyes blink open and briefly glow with a yellow magical light, as does the brass "W" letter upon the door, before returning to their dull brass patina. It is obvious that one should hold the brass knob as one says the passphrase. 

If the players say anything except the passphrase while holding onto the door, a Destructive Wave spell centred on the space just in front of the door affects everyone down the corridor for 30'. [If Withers is CR4, Constitution save of DC 13 for half.. otherwise consider upping the DC to either 15 or 17, if your party is over levelled.] 5d6 thunder + 5d6 necrotic + knocked prone. This also makes a very loud noise, alerting all nearby tomb dwarves and possibly the tomb guardian in 38A "Control room" the floor below, up to you. 

If the players move the WELCOME mat in front of Mr Withers' door, they see the next handout: Carved into the stone under the mat is the phrase "SPeak crETIN aND eNTEr". (Background: It's a play on the very famous LOTR "Speak Friend and Enter" Mines of Moria door puzzle.) The answer however is not Cretin (or any word in that sentence) and the Destructive Wave spell is triggered as normal with an incorrect guess.

The pass phrase is actually Acererak, an anagram of all the lowercase letters in the clue and of course Withers' boss. When Withers opens the door to his office, he may actually say something more reverential; a benediction to his master: "In every thought and wicked deed I serve only my master Acererak the Eternal, first of his name and master architect of both the tomb and my fate." This may be discovered by reading Withers' journals inside his office (not much use in front of the locked door) or may be overhead if the players can find to spy on Mr Withers gaining entry to his office.

Ask for perception, investigation or flat intelligence checks to provide some clues if the players become stuck. A high enough roll points out the two styles of letters in the carved message. 

Alternative spells to vary the challenge
An alternative spell to Destructive Wave's multi target attack would be a single target Immolation spell; naturally targeting the individual holding onto the door knob. In this case, perhaps increase the dex save to DC 15, so that it can trigger a few turns beyond the first.   If you want all the mean DM points, do both. Immolate the door knob holder and destructive wave anyone standing behind them. Or choose your own mischievous spell... perhaps a poison cloud that turns all the PCs skin and gear blue for a few days, so Mr Withers can see who dared try to enter his Office.

Feel free to allow a Knock spell (for 10min) or a Dispel Magic (treat the magic locking the door as a 7th level spell) if the PCs don't like puzzles or are struggling.

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Not running ToA
If you're not running the Tomb of Annihilation, don't have a Mr Withers or an Acererak, but still want to fit it in your game somehow, consider running it straight: The passphrase is "cretin" or "cretin enter" or "cretin and enter". Each is strictly true. Don't worry the players won't see Acererak's anagram leap out at them if you're not providing clues in that direction. If they do... you can just shrug and say "Well I'll be! Look at that, it does!" 

If you've provided clues as to the owner of the door, perhaps you have to say "cretin" in another language, or in a thick accent... there is wiggle room to be dastardly and get to have the trap fire off a couple times.