Designing a "good feature" for a game like (or similar mobile RPGs/Empire builders) depends on what part of the game you want to improve—the story, the community, or the "end-game" grind.
If you deploy two heroes with a historical or lore connection (e.g., a "King" and his "General"), they unlock a unique passive ability or a flashy "Dual Ultimate." Fate King [Final] [APK]
Players can raise heirs who then become "Advisors" for their main heroes, giving them stat boosts based on how they were raised (e.g., a "Scholar" heir boosts magic stats, a "Warrior" heir boosts physical attack). Designing a "good feature" for a game like
Instead of standard PvP where you just fight an AI-controlled team, let players a "King" and his "General")