Rulers, your intellect is very little
And your pride both big and brittle
If you would grow great and stately
Time to rule honestly and sedately

— Ed Greenwood (@TheEdVerse) May 9, 2020

1)
There are several sorts of mimics (intelligent, less-so “killer” mimics, and so on). The 5e designers just haven’t been bitten by (and so, reminded about) one of the smart ones yet. The ones who can lure by vocal mimicry, not just visual. Or as Dove once put it, 2)
…"If you must 'go' in unfamiliar surroundings, be rather careful about where you sit down."
(!)#Realmslore

— Ed Greenwood (@TheEdVerse) May 9, 2020

We have a mimic that travels with our party and if destroyed rebuilds it self, it takes the form of my Drow Princess’s travelling chest of drawers, and tends to steal and devour her high class sexy lingerie, she has reduced it to splinters on many occasions I do hope someone else in the party carries a few spare scanties for her, or she'll be lingerieless in the night on all too many important occasions.

— Ed Greenwood (@TheEdVerse) May 9, 2020

Pact Sacrifice: As an action, you can spend and roll a number of Hit Dice equal to the level of your warlock spell slots. You take damage equal to the number rolled and regain one spent warlock spell slot. It's clear to me that this is a big boon to warlocks in parties that rarely take short rests, and is less useful for warlocks in parties that rest often. Hey, fine by me!

— James ☂️ Haeck (@jamesjhaeck) May 29, 2020

So long as the damage cannot be prevented in any way, I think it's cool!

I'd almost rather it be a bonus action to make it better in combat. If essentially lose my turn to do this AND took damage, it's a less attractive option. As a BA, it could be an awesome Hail Mary move!

— Justice Arman 🐍 Darkhold Out Now 🦇 (@justice_arman) May 29, 2020

other than, “don’t,” what advice could you give me on DMing for a group of 9-10 PCs. Assuming you mean 9-10 individual players?

Keep in mind combat rounds will be very lengthy even if everyone moves pretty efficiently. Consider using a round table initiative order instead of rolling. Save yourself that work.

— Dan Dillon 👥 (@Dan_Dillon_1) February 21, 2020

Yes, 9-10 active PCs at the table at any given moment. I am running Descent into Avernus, and it’s my first hardcover. How much play do I have in terms of encounter difficulty since there are just so many PCs? What are some ways to make it challenging and still engaging?They will frogstomp almost every encounter unless you split the party into different encounters (run are the same time), or way increase the difficulty.

Increasing the difficulty will make encounters take an incredibly long time, most likely.

— Dan Dillon 👥 (@Dan_Dillon_1) February 21, 2020