Ms. Dorothy, known as Tome-san in the Japanese version, in the Japanese version, is a character in the Tag Force games. This is a video game version of the anime character, Ms. Dorothy.
The player can partner with Dorothy, but not immediatly - they must clear Part 3 with 5 different Tier 1 characters in order for her to become unlockable.
In Tag Force, the player will be given the choice to duel Dorothy using a "Dark Magician Girl" costume during the School Festival, as Dark Dorothy Girl, instead of the duel spirit - after the duel, Dorothy will mention being interested in duels enough to take part in the tournament, but she will remain unavailable for other duels outside of Free Duel mode. In Tag Force 2 and Tag Force 3, if the game was beaten with at least 5 Tier 1 characters, Dorothy can instead be dueled normally at any time and will agree to team up with the player after being defeated.
Dorothy is not a good character to team up with - she is ineffective as a partner, using extremely weak Decks specifically made to be a burden no matter what kind of Deck the player uses by wasting their cards to summon weak monsters, with the player being unable to remove or reduce the possibilities of it happening by editing her Deck due to every card in her Partner Decks being marked as favorites. This extends to the minigames as well - during the Dodgeball minigame, for example, Dorothy tosses only cream pies and does not move from her position. Should the player get knocked out, she will start playing normally, although she will still remain in her position.
Partnering with Dorothy is necessary in Tag Force if the player wishes to unlock every booster pack at the shop, as the pack "Dorothy's Soul" (which contains the majority of cards that increase Life Points) can only be unlocked by clearing Part 3 with Dorothy. In Tag Force 2 and Tag Force 3, however, there is no reward for finishing Story Mode with Dorothy other than obtaining her Deck Recipes.
Most of the Decks Dorothy uses in the first three games have little to no coherence or any way to win, such as running mostly high-Level monsters with no way to summon them, or nothing but cards that are helpful to her opponent while providing her no benefits. As a constant, however, most of her Decks feature "Dark Magician Girl".
There are some exceptions to the previous statement. Her last Deck in the second and third games are based on the Exchange of the Spirit OTK. The Deck used by Dorothy during her story in Tag Force 3 is also surprising - despite it containing nothing but Tuner Monsters and support cards for them, she has several useful Synchro Monsters in her Extra Deck which can be summoned by using the player's non-Tuner monsters.