During a 3.5 session perhaps 15 years ago, my players encountered two omnimentals (MM3) in an enormous dungeon. There might have been some sort of earthy wall between them and the players, with the gargantuan, flying elementals peeking over the top, launching elemental balls. Not that the wall posed much difficulty to the high-level characters.
An important thing to note about this huge chamber is the ceiling, which was at least a hundred feet tall, but probably quite bit taller. It was an underground area of cinematic proportions.
Killer art, standard for the Monster Manual III.
3.5's Monster Manual III, from whence I pulled the omnimental, has a special place in my heart. However, the reason this encounter was memorable was the nature by which the omnimentals were defeated.
They were crushed by celestial orca whales.
While the other characters distracted the omnimentals, the cleric used a summon monster spell to summon celestial orca whales in the air, high above the creatures. As the whales careened down onto the omnimentals from above, the party's wizard tried to use some spell to accelerate their speed, which I allowed. (I don't remember what the spell was.)
With the whales rapidly descending upon the omnimentals, the next question was how to calculate damage. At this point, my players broke from their seats around the table, huddled around a piece of paper, and began performing trigonometry and physics calculations. They cross-referenced their results with the game's rules. I believe the damage was well over 400 points each. Glorious victory.
Dungeons & Dragons typically eschews realism in favor of abstraction – a significant factor in the game's strength. There are few physics formulas in the rulebooks. But if, one evening, PCs deep within your milieu's underworld try to summon arial orca whales and magically accelerate their descent, consider letting it happen. And if your players leap up from their chairs and excitedly begin calculating hypotenuses and crushing damage, consider that a memory might be forged.
By the way, I don't know whether we were aware, at the time, that aquatic creatures like celestial orca whales cannot be summoned outside of an aquatic environment. If we knew, we happily ignored it for that encounter.