The monetization surface is unusually direct. Rolimon's lists passes for Double Roll, Fast Roll, Lucky Rolls, VIP, Auto Collect, More Drops, and extra equip capacity. Those products map cleanly onto the loop because they sell more attempts, better odds, less friction, and more team power.
The clean public read is simple: Slime RNG went from #264 Top Earning on Apr 23 to #21 by May 3. In the same window, visible player count rose from 3.3K to 82.4K.