Sester

Two and a Half, or Sester, is a Numberblock made of 2½ blocks.

Appearance
Two and a Half is gold with red limbs and lips. She has a 2 point crown and a grey bow.

As Two and a Half
Two and a Half appeared in 'Mixed Fractions' where she meets Three. She appears again later on where Three shows Number Bonds to 3 with mixed fractions.

As Sester
Sester debuted in episode 12 as her future self who killed future Vermone. She is later hit on the head with a time machine by a traumatised Olive.

In episode 13, Two Sesters (actually a revived Five), disguise as Judge Doom. Vermone was too clever for them. One of the Sesters slam the other on to the ground multiple times and rushes off.

In episode 14, Sester is desperate for water, showing that the place is a desert. She then turns into a giant, cycloptic, thirsty flower monster, scaring Four. It was then revealed to be a dream that cuts off at two scary monsters screaming at Four, meaning that Sester's monster Is not real.

In episode 16, Sester returns and turns Two into a baby, who turns into an old man later on. Sester nearly does it to Five, but she turns it around and then Sester turns into a smaller, green t-posing version of herself.

In episode 19, she is briefly seen in a room dead on the floor along with the Numberkids others. He is a Squidward's Baby

Trivia

 * Sester is responsible for many bad things, Scaring Four in a dream and slamming herself on to the ground multiple times. She has thankfully calmed down ever since.
 * Sester originally debuted in the scrapped episode 11, but the episode got scrapped due to loss of scripts, so she debuted in episode 12 instead.