Sonic Speed DX (ソニックのスピードDX Sonikku no Supīdo DX?) is a mobile phone game released as part of the Sonic Cafe service offered by Sega, and is the third version of a line of games whose predecessors were Speed and Speed DX. This game is a card game where players choose a character between Sonic, Tails, Knuckles, Amy Rose, Robotnik and Shadow, then either play a single-player game against the computer or a multiplayer game against each other. High-scores can be logged on the high-scores server. There is also a tutorial mode to explain the game's rules and a graphically cut-down version of the game for the lower-spec phones.
Each player is dealt five cards to form a hand, and fifteen cards facedown to form a drawing pile. A stack of five cards is then placed facedown on each side between the players, and serves as a replacement pile. Finally, two cards are placed between the replacement piles in the center in two different places, also facedown.
Players flip the two center cards and proceed to put down cards. After a card is played, another is drawn from the drawing pile to maintain five cards in the hand. In traditional Speed, a player cannot put down a card of the number (a nine cannot be placed on top of a nine), only a card one step higher or lower in value than the card in the center. For ace cards, the two choices are king and two.
The objective of the game is to be the first person to play all his or her cards. Players do not take turns, and may play as many cards in a row as possible. It is considered unfair to put down more than one card at a time, but one may place them immediately after each other. For example, one may not put down 3, 4, 5 in one motion, but they could put down 3 then 4 then 5, in three separate motions. If neither player can put down any cards, they flip cards from the replacement cards at the same time and continue.
If all cards are used up, the two piles are shuffled, and then used as the replacement decks. A card is drawn off of the top of each deck and play resumes.
- All the of the hero artwork in this game is recycled from Sonic Advance. Eggman's artwork is from Sonic Adventure and Shadow's artwork is from Sonic Adventure 2.