Restricted character creation is a pre-game selection of rules that adds additional gameplay mechanic(variant gameplay).
Usually these character modes are not implemented, but followed by players as convention.(though implementing them might balance this with perks to leveling speed or level-scaled bonus to attack/defense, so they are viable options).
1.Items restristions:A. Cannot use/trade items(naked mage) or B. use only non-magical(low-fantasy mode) or C.only cursed items(challenge equipment) or D. Cannot use consumables/potions(regen only) or E. can only use found items(living off the land).
2. Can only die once(permadeath) or permadeath from monsters only :Implemented in some RPGs as Hardcore mode.
3.Can't use fast travel/portals/waypoints.i.e. always walking A to B.(no fast travel challenge)
4.Restricted set of skills(e.g. cannot use defensive spells or curses) or use of only one skill(typically basic attack/caster spell).(one skill challenge)
5.Cannot attack intentionally(pacifist run). Effects from defensive procs(Chance to cast, defensive aura, perks,on-hit mechanics) may apply as damage to enemies.
6.Full clearing.i.e. each levels must be fully cleared of monsters and items to advanced to next level.(100% completion run)
7.Speedrun: the player has to complete the game as fast as possible.