Start with the R-pentomino
The R-pentomino begins with only five live cells inside a 3 x 3 bounding box, which makes it the clearest small methuselah to inspect by hand.
That tiny seed is famous because it does not settle quickly. It takes 1,103 generations to stabilize, ending with a final census of 116 cells and 6 escaping gliders.
Compare it with Acorn and Diehard
Acorn is another classic small methuselah, but it is not 3 x 3. It starts with seven cells in a 7 x 3 bounding box, lasts 5,206 generations, and stabilizes with 633 cells.
Diehard is useful because it teaches the opposite outcome. It starts with seven cells in an 8 x 3 bounding box, stays active for 130 generations, and then completely vanishes.
Edna shows the extreme end
Edna is not a beginner-sized 3x3 pattern. It starts with 149 cells in a 20 x 20 bounding box and lasts 31,192 generations.
Including Edna beside R-pentomino, Acorn, and Diehard helps separate two ideas: a methuselah can be small enough to inspect by hand, or large enough to act as an automated enumeration benchmark.
How to use the live pages
Start with the R-pentomino page and run the pattern slowly for the first few ticks. Then switch to Acorn for a long expansion, Diehard for extinction, and Edna for a much larger transient.
Use the pattern library search for terms such as 3x3 methuselah, R-pentomino, Acorn, Die Hard, Edna, 31192, and Gosper gun when you want to jump directly to a runnable pattern.
Working takeaway
Use R-pentomino as the compact 3 x 3 example, then use Acorn, Diehard, and Edna to show how methuselah behavior changes with seed size and outcome.