SudoKanard

 Killer/X-Sums Sudoku Apply classic Sudoku rules. The digits placed in each marked cage must sum to the total given in its top-left corner. Digits must not repeat in cages. Each clue outside the grid indicates the sum of the first digits placed in the corresponding direction, where X is equal to the first digit placed in that direction. Solve this puzzle on Penpa: https://tinyurl.com/2rybmlhj

 Killer/Quadruples Sudoku Standard Sudoku rules apply. Killer : the digits in a cage must sum to the number printed in its corner; digits may not repeat within a cage. Quadruples : circled digits where four cells meet must be present as values in those four cells. Solve on Penpa: https://tinyurl.com/22685wop Solve on SudokuPad:  https://tinyurl.com/y4uw5arv

 Killer Sudoku Standard Sudoku rules apply. Also, the sum of the digits in each cage must equal the value given in the upper-left corner of that cage. Digits cannot repeat inside a cage.   Penpa link:  https://git.io/Juki6

 Between Killer Sudoku Classic Sudoku rules apply. The digits in a cage must sum to the number printed in its corner. Digits may not repeat within a cage. Cells along lines between two filled circles must have values strictly between those in the circles. Solve on Penpa: https://tinyurl.com/yahtleg3 Solve on CtC: https://bit.ly/3qKzE8e Solution on video: https://www.youtube.com/watch?v=_-piQrp8pp4

 Killer Sudoku     Standard Sudoku rules apply. Each cage with a dashed outline contains different digits and their sum is given in the top left corner of the cage. Penpa link for online solve: https://tinyurl.com/ycvqq2ps

 49     Standard Sudoku rules apply. Little Killer: a number next to an arrow is the sum of all digits along the diagonal pointed by the arrow. Killer: in each cage with a dashed outline, the sum of all digits is written in the top left corner of the cage. Fortress: each digit in a green cell is greater that all digits in orthogonally adjacent white cells. Thermo: along each thermometer, digits strictly increase starting from the bulb. Sandwich: each number in the left margin of the grid is the sum of all digits sandwiched between digits 1 and 9 in the corresponding row. Skyscrapers: each number on top of the grid is the number of buildings visible in the corresponding direction (digits are viewed as building heights and higher buildings block smaller buildings from view). Penpa link: https://git.io/J1jmU

 All or Nothing Killer Sudoku Standard Sudoku rules apply. Killer Sudoku rules apply: in every cage with a dashed outline, all digits are different and the number that may be written in the top left corner is the sum of all digits in the cage. When the sum is written with two different digits, either both digits are in the cage or none of them are. This applies even to cages whose sum is not specified.   This variant was invented by Erwan Bernard. Penpa link to solve online: https://git.io/JlJwm This puzzle was solved by Simon Anthony on Cracking the Cryptic: https://www.youtube.com/watch?v=uVYG5Jica1I