I think you can simplify this and split it up into smaller restrictions so that people can pick the parts they like. Otherwise I don't think anyone would play this mode.
- "Cursed": Nerf to everything RNG based. Halved drop rate, dropped equips more likely to roll bad stats, halved scroll success rate, always gain the lowest possible HP/MP when you level, maybe quests/exchange/crafting have a 50% chance to give no rewards.
- "Punishing deaths": Safety charms not allowed and lose stuff when you die. I wouldn't make it take away slots because the 4 slots restriction already exists for that purpose. Instead make you lose a random equip (either currently equipped or from your equip tab), a random stack from your use tab, or half your mesos. Or maybe all three of those. If this mode is made too punishing then you might as well just pick hardcore instead.
- "Nightmare": You deal half damage and mobs deal double damage. You don't need to halve EVERYTHING as it effectively becomes a 4x or 8x nerf in some areas. For example if you deal half damage then it already costs twice as much in MP pots to deal the same amount of damage. Then if you also make pots cost double and heal half as much it's like an 8x nerf. I would not include exp, inventory slots, or stack sizes in this restriction either because half exp and 4 slots restrictions already exist for that.