Ultrabullet

At the tender age of 20, Penguingm1 is already one of the best hyperbullet and ultrabullet chess players in the world.

Source: wiktionary

Firouzja’s surprise loss to Fedoseev this week was partly attributed to his preference for 1+0 bullet without the one second per move increment. And there are plenty who consider even 1+0 bullet too slow, and prefer to play hyperbullet, 30 seconds, or ultrabullet, 15 seconds for the entire game without increment.

Source: wiktionary

Nakamura is a deadly performer at time rates ranging from 25-minute rapid right down to online "ultrabullet", where each player has 15 seconds for the entire game.

Source: wiktionary