Three Hundred, or 300 is a Numberblock made up of 300 blocks. Her first and only appearance was in One Thousand and One. She is voiced by Beth Chalmers.
Appearance
In One, Ten and One Hundred's imagination, she looks like a big Three, despite the lack of any juggling balls.
300 is a triangular number (1-24 added together). Despite this, she doesn't have a Step Squad mask. This is probably because the creators didn't check if 300 was a step squad, or that the trait is from her "base version", Three, who doesn't have a permanent step mask, but is seen wearing one occasionally.
It is possible that since 300 never had a physical appearance, her design may differ physically (Sixty-Four's design is different than her drawing in More to Explore, having eyebrows).
300 is the biggest numberblock to be a Step Squad.