The player can unlock this character by killing a total of 3000 Dragon Shrimps then purchasing with 500, which scales with other characters purchased.
Dragon Shrimps, Flame Dragon Shrimps, Serpentine Dragon Shrimps and Serpentine Flame Dragon Shrimps all count toward the kill requirement. However, the boss versions of Dragon Shrimps, the Colossal Bone Dragon and the Colossal Flame Dragon, and Serpentine Skeleton Dragons, which appear in The Bone Zone, do not.
O'Sole gains +1 Amount every 20 levels until level 60. The maximum Amount gained this way is +3.
The following table shows how much Amount it gains by level:
- O'Sole has no bonuses before level 20, making it particularly hard to start with compared to other characters. At level 20, O'Sole, along with Mortaccio, Cavallo, and Ramba, will be comparable to Gennaro, as both have +1 Amount.
- O'Sole, Mortaccio, Cavallo and Ramba all have identical passives and stats and only differ in starting weapons.
- Once per run, typing "pet" while using O'Sole summons a ring of little hearts that heals it.
- O'Sole cannot be damaged by the plants in Il Molise, mainly to compensate for the fact that the weapon can only fire backwards and cannot actually deal damage to the plants.
- O'Sole, Mortaccio, Cavallo, Ramba, and Ambrojoe are able to get the highest persistent Amount in the game at level 60 with 2 levels of Duplicator and the Amount PowerUp, adding a total of +6 projectiles to all applicable weapons.
- Ambrojoe gains +10 Amount as a starting bonus, but quickly loses said Amount as they level up.
- The name most likely references "'O sole mio", a popular Neapolitan song.
- The character is probably a reference to the protagonist of the Okami game series, Amaterasu, who is the Japanese sun goddess in the form of a white wolf, that uses the Celestial Brush to conjure her godly powers and spawns flowers when running, just like the weapon Celestial Dusting. In addition, O'Sole Meeo's theme song, which is also used by Giovanna, uses traditional Japanese/Asian instruments.
- "O'Sole Mio" literally translates to "My Sunshine", adding another layer of reference to the Goddess of the Sun.
- The Spell to unlock O'Sole is "Reset", which is the name of the song that plays during Okami's credits.
- While O'Sole and Giovanna's theme songs are the same, O'Sole's theme song differs slightly from Giovanna's in that it starts off at normal speed, whereas Giovanna's theme song starts off slower.