None of this would affect online rank multiplayer but however it could make scenarios far more exciting. Some of these RPG mechanics could still be used in multiplayer lobbies.
Inventory. Allows you to select items such as healing potions, cure poison, or weapons to change their stats. Two handed weapon more damage, one handed with shield more defense. Use a bow instead of melee weapon. Magical ring. Allows you to block melee attack every five seconds, ring of regeneration heal health. Equip a better armor.
Spell book. Allows a cleric or Mage to cast spells. Cleric focus on healing spells and buffing allies. Lacks offensive spells, however they the ability to weaken undead, like zombies and skeleton warriors. Cleric unlock their spells automatically from leveling up, don’t need to read scrolls. A mage focuses on crowd control and more offensive magic, and summoning monsters.
The more “experience” from quests or killing enemies the more spells you unlock. Spells scrolls for mage can be found in chests or containers to unlock spells. However if the spell is too high level for the Mage can’t use them, until he reaches the appropriate level.
Pickpocket for thieves. Allows a thief character to rob item from a unit. However it is a dice roll, sometimes you get caught the unit will attack you.
Dialogue options. When you’re character enters dialogue with a character. You could barter with them, insult them and they turn hostile, or increase or decrease repetition depending on what you say. This could result in consequences in the in the scenario such as additional hostiles on the map because of your actions. Certain factions will not be friendly or be friendly towards you. Price increase or decrease from merchants.
Inns. Allows you to recruit units (heroes and whatever) engage in gossip by drinking beer. However this can debuff your stats for a while, in exchange you get information from rumors and stuff like this. You might even befriend a character who will give you a free item ending on your dialogue choices. You can also rest in Inns to gain a buff in stats, if your have not been in for a Inn for long time you get a debuff from exhaustion.
Visiting a church, the priest can cast healing spells and get rid of some debuffs, and also resurrect dead characters that you’ve lost on your adventures.