Nitro-999 was a "souped-up" version of Nitro-9 created by Ace. However, the timers still needed work.
In 2022, Ace brought canisters of Nitro-999 with her to the Daleks volcano base to destroy it. The Holo-Doctor expressed appreciation for the explosive, commenting that it was just what they needed. Ace and Graham O'Brien used the explosive to destroy a Bronze Dalek before planting the Nitro-999 around the Dalek base. As the Thirteenth Doctor rescued the two in the TARDIS, the Nitro-999 exploded, destroying the Dalek base and all of the Dalek forces on Earth. (TV: The Power of the Doctor [+]Loading...["The Power of the Doctor (TV story)"])