#A37: FiveCells

 Not counting rotations and reflections as different, there are exactly 12 pentominoes, which might be why this type was chosen for the twelfth day instead of FourCells. I prefer this type to Pentominous because it doesn't tend to lead itself into extensive bifurcations. I really like the technique this shares with Heteromino and FourCells, but I wasn't exactly able to include it in these puzzles.

https://puzz.link/p?fivecells/10/6/b1d2m1a1a2a2d2a2a0a.a1g.b2g2

https://puzz.link/p?fivecells/12/12/7a12a12a12a7n12e12f12b12a2l12a1212a12m12a12b12a12n12121212n7j7