Mental Prison: can I use Dimension Door to avoid the psychic damage?

If a lvl 11 PC gets a sidekick, it would make sense for the sidekick to be lvl 11 right?

If you’re concentrating on a spell and you cast another concentration spell, does the first spell end *immediately* upon casting?

Shadow of Moil spell makes the warlock heavily obscured…

Do Mastery of Death or Strength of the Grave function like Death Ward?