Costume stats that give 50 procent attack and 2 procent zed gain
Ability stats can be upgraded with diamonds (real money) so you can basically have 300 procent all base stats if someone spends like 10k (idk numbers) You can at least get that slowly with zed as well
VIP system where vip silver needs 500000 points (i strongly assume 1 diamond spent or recharged equals 1 point) Silver gives costume bracelets that gives 25 procent atk dmg and 5 zed gain (you get two so i assume you can equip both for imba 50 procent atk gain)
VIP gold is likely way more expensive than silver and plat way more expensive than gold. Plat VIP also gives an infinity healing pot
Pet needed to pick up items, but said pet also needs cash shop food to do that.
You are very likely going to need permanent bag spaces as well (that would by itself be ok if all the things above was not a thing) to play the game without needing to sell all the time
You can buy auto battle time with real money, so you dont need to manually grind.
At this point Maplestory M is a better game