I like the little world you created here, and really accessible gameplay. Though at first I was confused -- I thought I was supposed to do a puzzle game in the left side to attack the monsters.
For some ideas on RNG, check out how Tetris has done it over the years: https://simon.lc/the-history-of-tetris-randomizers
I usually use some variation of the "7-bag" to balance things out for all my randomness.