Levels and prestige
Everything you do gives XP: killing mobs, finishing quests, mining. Each level raises your stat caps, so a level 30 character survives fights that kill a level 5 one.
The ceiling is level 300. Reaching it is not the end: prestige resets your level back to 1 and lets you climb again, keeping a permanent mark that you did it. There are three prestiges. Your total XP never resets — that is what the XP leaderboard ranks.
There is no passive healing. Food, potions and perks are the only way back up after a bad fight, which is why the economy matters from the first day.