Congratulations on the finished game
The idea sounds interesting
There are 2 factors in the game that make life difficult for the player and it seems to me that only one of them works well now
1) the game constantly makes you look for a new face - this is interesting and makes you actively look for your twin in the crowd
2) due to the fact that the player grows in size, it becomes almost impossible to get to your twin, who constantly hangs out in the company of the same small creatures - the arena is small and you can't get around the crowd from any side, which makes the game very offensive and unfair after 2 successful merges
My suggestions for solving the second problem could be - hard collisions for creatures so that they do not pass through each other and move in predictable bouncing trajectories, so the player can calculate how the situation will look in a couple of seconds
And also make the arena bigger, now there is little space very quickly
Maybe renew all the player's lives after each merge? As a reward