Here are four puzzles each containing 4 pentacubes.
There are four objects to be constructed, "keys", made from assemblies of 20 cubes The objects are related, each has a bottom layer of 16 cubes arranged in a square. A second layer contains 4 additional cubes as follows:
Key_Corner has the four cubes at the corners of the first layer
Key_Diagonal - the four cubes form a diagonal across the first layer
Key_Center has the 4 cubes as a square centered atop the first layer
Key_Edge has the 4 cubes as a square centered at the edge of the first layer
(Note - there are 460 other ways to arrange the 4 cubes atop the first layer.)
Corner_puz_3 constructs both Key Corner and Key_Diagonal
Diagonal_puz_32 constructs both Key Corner and Key_Diagonal
Diagonal_puz_6 constructs Key_Diagonal, Key_Center, and Key Edge
Corner_puz_14 constructs Key_Corner and Key Center
Assemble_pieces.scad contains a description of how the puzzles were created, explains the numbering of the puzzles, contains additional puzzles, and can construct the 460 other keys.
The puzzles and keys can all be printed in draft mode without support.
A tiling search was used to construct these puzzles see - tiling-04.tar - at http://djm.cc/dmoews.html
Constructing the puzzles is a pleasant exercise as the four cubes on the second level provide a useful clue. Two of the pentacubes in Corner_puz_3 and Diagonal_puz_32 are mirror images. Interesting pairs of solutions are found if both are used to construct the same key.
Puzzle_answers.scad shows answers to the four puzzles plus answers to several additional puzzles. These puzzles are similar to those at
https://www.thingiverse.com/thing:3533020 "Puzzles from Pentacubes".