Here’s my first contribution to 2024’s competitive puzzle calendar. I wrote a round for the UKPA Open Puzzle Tournament which happened last weekend. The round concept was based on a puzzle I made for last year’s EnigMarch.

That puzzle was instructionless, so if you want to solve it that way, do that now before continuing to read. The idea was to add a clue type to Snake which allows the path to branch (into a hydra). All other rules were just regular Snake. Ever since writing that puzzle, I’ve been meaning to make a puzzle pack by applying this Hydra variant to various existing snake genres (of which there are plenty). A contest round seemed like a great excuse to finally do this. So the idea was to pick a bunch of snake genres and write one puzzle with the regular rules and one puzzle with the Hydra variant.

We decided to present the round simply as pairs of Hydra puzzles (which works since a Hydra puzzle without sword clues just becomes a Snake), both for cutting the number of examples and rulesets in half, and also as a small surprise for the participants. So even though the surprise is gone, this is how I’m presenting the puzzles here: all puzzles are labelled as hydras, even though the first of each pair is actually a snake.

I mostly went for easier puzzles this time around (since I wanted to fit a lot of puzzles into an hour) but there’s still a variety of difficulties. You can find a solved example puzzle before each pair below. A couple of notes about the Penpa versions: all puzzles expect grey shading for the answer check, except Persistence/Dyarchies of Memory, which you can alternatively solve by drawing a line along the snake or hydra (your choice). I also had to change the presentation of that genre and Belarusian Snake/Hydra to use cages instead of shaded regions, because Penpa does not seem to like shading answer check when the puzzle already has shaded cells.

At the very bottom of the post you’ll find a **bonus puzzle**. I was originally going to include a Myopia variant instead of Bosnian Snake. However, after making the snake puzzle, I just couldn’t find a satisfying way to construct the hydra I wanted. Whatever I tried, I had to add some disambiguating clues or swords near the end that created huge shortcuts for all the interesting logic I had set up earlier. Maybe one day. In the meantime, there’s a small example hydra and a regular-sized snake puzzle to enjoy.

Hydra

Solve it online:

**Rules:** Shade some cells to form a hydra. No 2x2 can be entirely shaded, and there are no 4-way junctions of shaded cells. Swords mark all cells which contain a 3-way junction of shaded cells. All unshaded cells are orthogonally connected to the edge of the grid. Black circles are shaded and must lie on an endpoint of the hydra. White circles are shaded but must not be an endpoint. A number outside the grid represents how many cells in the corresponding row or column are shaded.

Solve it online:

Bosnian Hydra

Solve it online:

**Rules:** Shade some cells to form a hydra. No 2x2 can be entirely shaded, and there are no 4-way junctions of shaded cells. Swords mark all cells which contain a 3-way junction of shaded cells. All unshaded cells are orthogonally connected to the edge of the grid. Black circles must lie on one endpoint of the hydra. Number clues cannot be shaded, and represent the number of shaded cells in the (up to) eight cells surrounding the clue.

Solve it online:

Solve it online:

Dyarchies of Memory

Solve it online:

**Rules:** Shade some cells to form a hydra. No 2x2 can be entirely shaded, and there are no 4-way junctions of shaded cells. Swords mark all cells which contain a 3-way junction of shaded cells. All unshaded cells are orthogonally connected to the edge of the grid. Black circles must lie on one endpoint of the hydra. Every cage contains at least one cell of the hydra. If two cages are the same shape and orientation, their contents must be identical (including where the hydra crosses the cage’s border).

Solve it online:

Solve it online:

Belarusian Hydra

Solve it online:

**Rules:** Shade some cells to form a hydra. No 2x2 can be entirely shaded, and there are no 4-way junctions of shaded cells. Swords mark all cells which contain a 3-way junction of shaded cells. All unshaded cells are orthogonally connected to the edge of the grid. Each region contains exactly three shaded cells. All regions containing at least one endpoint of the hydra are marked with a cage.

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Solve it online:

First Seen Hydra

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**Rules:** Shade some cells to form a hydra. No 2x2 can be entirely shaded, and there are no 4-way junctions of shaded cells. Swords mark all cells which contain a 3-way junction of shaded cells. All unshaded cells are orthogonally connected to the edge of the grid. Black circles must lie on one endpoint of the hydra. A number outside the grid represents the length of the first run of consecutive shaded cells in the corresponding row or column from the direction of the clue.

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Solve it online:

Hydra Egg

Solve it online:

**Rules:** Shade some cells to form a hydra. The shaded cells cannot form any loops (including 2x2s) but may touch diagonally. There are no 4-way junctions of shaded cells. Swords mark all cells which contain a 3-way junction of shaded cells. Black circles must lie on one endpoint of the hydra. Exactly one orthogonally connected area of unshaded cells must exist of each size from the range given outside the grid. Cells with number clues cannot be shaded, and represent the size of the area they’re in.

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Solve it online:

Sea Hydra

Solve it online:

**Rules:** Shade some cells to form a hydra. The shaded cells cannot form any loops (including 2x2s) but may touch diagonally. There are no 4-way junctions of shaded cells. Swords mark all cells which contain a 3-way junction of shaded cells. Black circles must lie on one endpoint of the hydra. Clues cannot be shaded, and represent the total number of shaded cells that appear in the indicated directions.

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Solve it online:

Bonus: Myopic Hydra

Solve it online:

**Rules:** Shade some cells to form a hydra. No 2x2 can be entirely shaded, and there are no 4-way junctions of shaded cells. Swords mark all cells which contain a 3-way junction of shaded cells. All unshaded cells are orthogonally connected to the edge of the grid. Black circles must lie on one endpoint of the hydra. Clued cells cannot be shaded, and contain arrows indicating all of the orthogonal directions in which a shaded cell appears closest to the clued cell. At least one shaded cell must appear in the direction of an arrow.

Solve it online: