for things like changing your gamemode without essentials you'd have to type /gamemode creative, survival, spectator, or adventure
for gravy you need NBTApi if you don't already have it, DeathMessagesPrime may not of been updated yet if it has been updated by the dev but the newest version hasn't been added to minehut you can suggest it here https://forums.minehut.com/forum/20-plugins/ for Armor Stand Editor if you'd like here's a tutorial you can watch if that helps