Logic Masters Deutschland e.V.

This is my entry for turn 7 of season 1 of The Skunkworks League, hosted by damasosos92. In this round, the prompt was to create a quattroquadri puzzle using only standard local constraints, with a target difficulty of 2 or 3 stars. At least 8 different constraints must be used, and each constraint type can only be used once.

Rules:
Quattroquadri: Place the digits 1 to 9 once each into the 3x3 boxes. Digits may not repeat in the same row, column, or box.

Standard X pairs, Kropki pairs, Arrow, German Whispers, Renban, Region Sum Line, Entropic Line, Modular Line, and Numbered Rooms rules apply.

X Pairs: Digits separated by an X sum to 10.

Kropki Pairs: Digits separated by a black dot must be in a 2:1 ratio. Digits separated by a white dot must be consecutive.

Arrow: Digits on an arrow must sum to the digit placed in that arrow's circle.

German Whispers: Adjacent digits on a green line (also marked with a G) must have a difference of at least 5.

Renban: Digits placed on a purple line (also marked with an R) must be a non-repeating set of consecutive digits, in any order.

Region Sum Lines: 3x3 box borders divide blue lines (also marked with an S) into segments with equal sums.

Entropic Lines: Each set of three adjacent digits along a beige line (also marked with an E) must be one low [123], one medium [456], and one high digit [789].

Modular Lines: Each set of three adjacent digits along a teal line (also marked with an M) must be one each from the sets [147], [258], and [369].

Numbered Rooms: A clue outside the grid indicates the digit which has to be placed in the Nth cell in the corresponding direction, where N is the digit placed in the first cell in that direction.