The bi-block is a common formation of two blocks and the smallest and most common pseudo still life. Similar pseudo still lifes can be formed by considering any rectangular array of blocks, some of which are shown below.
The bi-block is about ¼ as common as the pond, the most common 8-bit strict still life. Compared to other strict still lifes, it is more common than the ship-tie but less common than the long boat. In odd orthogonal symmetries, bi-blocks are more common, as gliders in the same phase that collide in odd symmetry form a bi-block.
Counting both strict and pseudo still lifes, the tri-block is the 9th most common 12-bit still life, and it would rank third behind the ship-tie and mirrored table but ahead of the block on cap if it were strict. Unlike the bi-block, tri-blocks must form by chance.