The player base of gacha games can fluctuate over time based on updates, events, and changes in player interest. However, as of my last update in 2021, some of the gacha games with the most substantial player bases include "Puzzle & Dragons," "Fate/Grand Order," "Fire Emblem Heroes," "Genshin Impact," and "Dragon Ball Z: Dokkan Battle." It's essential to check up-to-date metrics and sources for the most current information, as the mobile gaming landscape can change rapidly.