Okay, here is my pitch for the opening sequence, taking queues from GotG and Indiana Jones, rather than a standard Hero's Journey 1st level character raised on a farm/in a library/in a luxurious underground mansion.
The camera sours over mountains, focusing on what appears to be a volcano the sound of clanging swords and fizzing spells can be heard faintly in the background. The camera zooms through the solid stone, and we see, initially a top down view, then focusing in closely on a party of four adventurers running through a tunnel, fighting a running battle against monstrous humanoids, whilst trading wisecracks (one of them is a dragonborn, since that is the easiest way to shoehorn in a dragon). Okay, so I may have borrowed a bit from the beginning of The Two Towers...
Suddenly the passage opens out, and the adventurers find themselves on a ledge above a pool of boiling mud. Wooden disks hang on chains from the ceiling. Yes, we are in White Plume Mountain, one of the most recognisable classic dungeons.
Traversing the wooden platforms (as the heroic music gets louder in the background) the party runs down more passages, finding themselves in a transparent underwater dome. Okay, I have moved rooms around a bit.
Grabbing the McGuffin of Doom from its pedestal, a huge crab-monster emerges from the shadows. One of the adventurers shoots an arrow at the crab, and it is deflected off it's armour and through the transparent dome. "Oh f....!" As boiling water pours in a cooks the crab the wizard bangs her staff to the floor and summons a bubble of force which surrounds the party.
As the heroic theme music gets louder, the party tumble around inside the bubble as it is propelled through a twisting series of tunnels, to eventually shoot out of the top of a volcano.
Title card: DUNGEONS & DRAGONS
Whatever happens next, I don't think that would leave anyone in any doubt. The D&D players will know it's an authentic D&D movie, and everyone else will have been shown what D&D is.