Soul Vessel

Give it to Strowen in Things Betwixt to reallocate your levels.

Where to find it

Finite: one from Saulden once four people live in Majula, plus chests in the Lost Bastille, Drangleic Castle, Memory of Orro and DLC areas.

Forest of Fallen Giants: Kill the skeletons under the map room for a Human Effigy, then take the Estus Flask Shard and the Soul Vessel from the chest
The Lost Bastille / Belfry Luna: A Pharros' Lockstone opens a hidden room with a Soul Vessel
Huntsman's Copse / Undead Purgatory: Once four new residents have moved to Majula, Crestfallen Saulden hands you a Soul Vessel; check back with him now and then
Drangleic Castle / King's Passage: Ride the lift up; the cage there needs a key from later. Chests hold the Key to King's Passage, a Soul Vessel, a Fire Seed and Strong Magic Shield
Undead Crypt: Back up, open the chest for a Soul Vessel and climb for a Soul of a Hero
Memory of Orro: Drop through the hole for Wilted Dusk Herbs, then down for a Soul of a Great Hero and Soul Vessel
Dragon's Sanctum: Loot this room's chests (Titanite Slab, Soul Vessel, Catarina Helm, Old Growth Balms, Destructive Greatarrows); next door a trapped chest gives Dried Roots
Brume Tower: Pull the lever for the giant door, go left, smash ash figures for Old Mundane Stones, take Lloyd's Talismans and open the illusory wall for Old Radiant Lifegems, Wilted Dusk Herbs and Soul Vessels
Frozen Eleum Loyce: Roof chests: Soul Vessel, Sorcerer's Twinblade and Divine Blessings