At one point during development Singlets was supposed to have a dual-type Psychic/Steel cross-generational evolution named Rerollan.
Singlets has Pokédex number 109, with no matching numbers. Dubus has number 110, with two matching numbers. Tripsius has 111, with three matching numbers. *clap clap*
The mfw as seen on its back is used to show anger that the post didn't get anything special.
Singlets evolutionary lines designs come from GETs, or where a post number ends in a large number of repeating digits or possibly in a unique sequence (for example; 1234567 would be a GET) Singlets represents a single GET, or a post number ending in only a single digit with no repeats.
It also is based on a coin, which one would put into a slot machine.