Ancalagon
Dusty Dragon
Why?
Because the new monster format has monsters not actually casting spells
comicbook.com
Because the new monster format has monsters not actually casting spells

Dungeons & Dragons Just Nerfed One of Its Most Popular Spells
A recent design change in Dungeons & Dragons had some unexpected consequences on a popular spell. The Wild Beyond the Witchlight introduced retooled statblocks for NPCs and spellcasting monsters, with a goal of making their damage output more in line with their Challenge Rating and to streamline...

Going back to the example in the first paragraph, a Level 5 PC could easily shut down that evil sorcerer trying to fireball his party, provided that the sorcerer was within range and the PC was ready to burn a 3rd level spell slot. However, they wouldn't be able to stop a "Fiery Explosion" action, as the description for that action does not describe it as a spell.