Painful Combat Only (PainCO) is a community created Game Mode, where a player's Character is only allowed to use combat skills in Hardcore mode. This means the player will only be allowed to level Attack, Strength, Defence, Hitpoints, Ranged, Magic, Prayer, and Slayer.
Furthermore, the player is not allowed to use the Shop, and equipment upgrades are illegal. Not only this, but you are not allowed to kill any Plants.
Another restriction is that you will not be able to equip the Amulet of Looting at any point, and due to the shop lock, the player won't be able to purchase Loot Container Stacking either.
Due to these limitations, the player will have no easy source of food or regeneration until they manage to sustainably kill Sweaty Monsters.
Because of this, the player will need to grind enough experience to reduce the enemy's hit chance greatly. This can be done by hitting enemies, without actually killing them. Since you're at risk of dying yourself, you must have a faster attack speed than the enemy, land a hit, and run away.
This can in theory be done starting a route at Golbin in order to get a Bronze Battleaxe, in order to reduce the attack speed to 3.1s. Note that you can kill up to around 3 Golbins per run, until you die. The chance of getting the battleaxe is 1 in 27.
Once you manage to get yourself your first weapon, hopefully with some health left, you may start farming experience at the Confused Pirate which has an attack speed of 3.1s, by repeatedly starting combat, and running away in the 0.5s gap until the pirate hits you back.
Eventually, you will be able to consistently get food from Sweaty Monsters, and from that point on it is similar to HCCO, except you will not be able to get any Damage Reduction until way later in the game, and it requires quite more manual gameplay to farm food.