Thirty-Six is a Numberblock made of 36 blocks. They were mentioned on We're Going on a Square Hunt as 6x6, but officially appeared later in The Big One as a compound Numberblock. This continues until in More To Explore where their figured-out form appeared as a drawing.
Compound form: Thirty-Six is a Thirty and a Six combined.
Figured-out form: It is unknown if it's official, well in Six's drawing, they have a pink step-shaped mask because they are the 8th step squad. They also have square eyes because 36 is 6x6.
Fan art/Fanmade designs
Zero, One, Two, Three, Four, Five, Six, Seven, Eight, Nine, Ten, Eleven, Twelve, Thirteen, Fourteen, Fifteen, Sixteen, Seventeen, Eighteen, Nineteen, Twenty, Twenty-One, Twenty-Two, Twenty-Five, Thirty, Forty, Fifty, Sixty, Seventy, Eighty, Ninety, One Hundred, One Thousand, Ten Thousand, One Hundred Thousand, One Million
Big Bad Square, The Terrible Twos, Octoblock, The Three Threes, Octonaughty, Step Squad, The Four Fours
Twenty-Three, Twenty-Four, Thirty-Five, Thirty-Six, Forty-Two, Forty-Nine, Sixty-Four, Ninety-Nine, Two Hundred, Three Hundred
Flapjack Snaffler, Blockzilla, Big Tum
Fluffies, Squarey, Numberblobs, Aliens, Rainbows, Flatlanders, Alphablocks