As of v1.0.0, the seed is the number of seconds since the Switch's boot when the game was started.
The egg and D4 solutions are both generated when save data is initialised, which is done right after selecting the difficulty level. The values on this page assume that the player has not triggered save data resets more than once. In other words, do not go back after confirming the difficulty level.
For instructions and explanations, please refer to the RNG Manipulation Primer.
Reminder: Because of precision issues the actual seed might be ±1 or even ±2 your expected seed value. To save time you should check your seed with the D4 puzzle solution.
The most common seeds are highlighted in red.