So, 16 creatures, each 1/1 would be blocked entirely (square root of 1 hp is 1).
8 creatures, each 2/2 would be dealing 1 damage each (square root of 2 hp is 1.41... but it's rounded to 1).
4 creatures, each 4/4 would be dealing 2 damage each (square root of 4 hp is 2).
2 creatures, each 8/8 would be dealing 5 damage each (square root of 8 is 2.83... so rounded to 3).
1 creature 16/16 would be dealing 12 damage (square root of 16 is 4).
16 x 1/1 -> 0
8 x 2/2 -> 8
4 x 4/4 -> 8
2 x 8/8 -> 10
1 x 16x16 -> 12
Seems like the Fusion used on opposing creatures is actually harmful. Unless you rewind that creature