Here are my suggestion.
1. Costume - costume with stat boost looks cool. Lets make the game more enjoyable and fun with this cool costume.
2. Land of Chaos and Soul Square - When entering 2 or more attempt drop rate and exp should increase by atleast 1.5 or 2x too. You only just increase the keys needed but not the drop rate and exp. Be considerate to the player please.
3. Prison of Greed - Let the Guard Respawn fast and move fast. When doing 3 or more attepmt using BD, drop rate and exp increase too.
4. Babel - Event itself is fun , but please improve the rewards. Honestly grinding for 10 mins is much worth it than the rewards in babel.
5. Obsidian - boosting from lvl 1 - lvl 2 (if failed still lvl 1)
boosting from lvl 2 - lvl 5 ( downgrade by 1 lvl / failed)
boosting from lvl 5 - lvl 7 (if failed back to lvl 0)
6. GVG - +10% attack and def on all attacking guild / winning streak of occupying guild is imbalance. Please change it to +10% atk to attaking guild and +5% or 3% def to occupying guild for every winning streak which is more balance.
7. Looting System - Rolling a dice or Random loot option when in party.
8. Guild Skill Boost - increase Patk , Def and HP of player.
9. Vault - Let the player store Diamond and Gold in vault.
Thats all for today sir, hehe! Happy leveling!