Dr. Luigi

Dr. Luigi is the sixth installment in the Dr. Mario series. The game was released exclusively for the Nintendo eShop on the Wii U as part of the Year of Luigi. As the title suggests, the game stars Luigi in a game very similar to Dr. Mario. Unlike his brother, Dr. Luigi still wears his signature cap rather than a head mirror, although later in Dr. Mario: Miracle Cure, Luigi wears the head mirror.

Gameplay
The gameplay is very similar to the original Dr. Mario game. Players must eliminate viruses by stacking Capsules on them so that a row of four or more of the same color is created. The objective for all the game modes is to eliminate all the viruses in the bottle, and in the multiplayer modes, be the first to eliminate all the viruses in the bottle. If the capsules stacked up to one of two middle columns in the topmost row, usually a capsule, the next capsule is blocked, causing the player to lose. In multiplayer games, losing this way is an automatic victory for the opponent. As a first in the Dr. Mario series, if a capsule is within a narrow gap and thus cannot rotate horizontally while vertical (or vice versa), rotating it will cause the colors of the capsule to switch places. This only applies to Retro Remedy.

In this game, there is a new game mode called Operation L that involves the use of L-capsules, which are multicolored L-shaped capsules in reference to Luigi's initial. Rather than controlling a single capsule piece with two halves, the player controls two capsules (each with two halves) held together in a blister pack so that they form the letter "L". After any part of the L-capsule lands on something, the blister pack will disappear, which causes the individual capsules to fall if they are not supported. If a capsule match is made after the L-capsule lands, the match will take priority, otherwise the capsules will succumb to gravity. Because of the larger capsule pack in Operation L, if one of the two middle columns in one of the two topmost rows is occupied from stacked capsules, the player will lose when the next piece is brought into the bottle.

The pattern of colors for the L-capsules is different based on the speed selected in the settings. For the Low and Med settings, the set of capsules will consist of three pieces of one color and one piece of another color, where the three pieces are the vertical capsule and the half of the horizontal capsule that touches the vertical capsule. For the High setting, the color configuration is that both halves of one capsule has one color and the other capsule has another color on both halves, resulting in two pieces of each color. Similar to single capsules in other modes, both parts of the pattern can be of the same color.

The result of a combo behaves differently for Operation L. In Retro Remedy (which consists of the classic Dr. Mario gameplay), after a player created a combo of multiple matching lines cleared in a single move, the opponent will receive two to four half-capsules based on the amount of capsule matches. In Operation L however, when a player performed a combo of multiple matching lines cleared in a single move, the opposing player's upcoming capsule will have its colors changed. Another difference is the speed in which stray capsules fall after they are split: the speed in which stray capsules drop in Operation L is fast, akin to holding down for dropping the capsule; On the other hand, the speed of falling capsule pieces in Retro Remedy is similar to previous games, where the pieces fall more slowly, akin to leaving a capsule to fall on its own at High speed.

Another difference between the two modes is the amount of viruses. The amount of viruses for each level in Operation L is different from Retro Remedy. Both of them start with 4 viruses at level 0, but while the latter adds 4 more viruses for every extra level, the former only adds 1 extra virus per extra level. For example, at level 20, Retro Remedy starts with 84 viruses (4 + 20 * 4), while Operation L starts with 24 viruses (4 + 20 * 1) at the same level. The maximum amount of viruses that appear at the beginning of the level is 40 viruses in Operation L, and 96 viruses in Retro Remedy, which are reached at the minimum level of 36 and 23 respectively.

Like Dr. Mario Online Rx, if the player completes the 5th, 10th, 15th, or 20th level in the Med or High speed, or only the 20th level in the Low speed, a cutscene will be played, and completing the 20th level at High speed in Classic one-player mode will result in the credits rolling. The credits can be viewed again from the menu after viewing it once. Also, if the player has reached a level higher than 20 in Classic (applies to both Operation L and Retro Remedy) or Virus Buster, they can continue from that level, but only for that specific mode and Speed / Difficulty. In other words, the level progress is separately tracked for each combination of mode and Speed / Difficulty.

On occasion, the player will have the option to post on Miiverse after completing a stage. As the service was shut down in November 2017, nothing can be posted there since then.

Game modes
The music selection is between Dizzy, Drowsy, a random selection between both themes, or to disable music for Operation L, whereas it is Fever, Chill, a random selection between both themes, or to disable music for both Retro Remedy and Virus Buster, though for the latter, the rendition of the theme is slower and calmer.
 * Operation L: The new mode in Dr. Luigi. In this mode, players use L-capsules to eliminate viruses.
 * Retro Remedy: This is the classic mode of Dr. Mario. Similar to Operation L, the player uses capsules to eliminate viruses. However, the player uses normal capsules to eliminate viruses.
 * Virus Buster: In this mode, only touch-screen controls are used. After a while on the same stage, two capsules appear, and then three. The gameplay is similar to the Virus Buster mode in Dr. Mario Online Rx. The GamePad's display can be switched between vertically or horizontally by pressing the button.
 * Online Battle: Like Dr. Mario Online Rx, the player can play with friends, or play with other players around the world in a Worldwide game. For Worldwide, the game's matchmaking will attempt to match up with a player of a comparable rating, though if it takes too long a player of a higher difference in rating will be matched up with. The modes available are Operation L and Retro Remedy.

Sub modes
In both Operation L and Retro Remedy, there are three modes:
 * Classic: Eliminate all the viruses in the bottle. In the 2 Player modes, be the first to eliminate all viruses in the bottle.
 * Vs. CPU: Only available in the 1 Player modes. Compete against the CPU to be the first to eliminate all viruses in the bottle.
 * Flash: Be the first to eliminate all three flashing viruses, one of each color, to win. In the 1 Player modes, the player compete against a CPU player. There are three difficulties that determine the amount of viruses in the bottle including the three flashing viruses. For Easy, Normal, and Difficult respectively, the amount of viruses are 14, 18, and 22 in Operation L, whereas it's 28, 40 and 52 for Retro Remedy.

Options
The settings for each game mode is saved separately.
 * Quick Drop: Only in both Operation L and Retro Remedy. Enables the ability to instantly drop a capsule.
 * Capsule Ghost Image: Only in both Operation L and Retro Remedy. Enables a preview of the capsule landing spot.
 * Virus Design: Sets the virus design in the playing field. "A" is the virus designs introduced in Dr. Mario, while "B" is the virus designs introduced in this game. The default for Retro Remedy is "A", while the default for both Operation L and Virus Buster is "B".
 * Writing Hand: Only in Virus Buster. Changes the orientation of the vertical display based on the writing hand. When using the vertical display, the left-handed option will rotate the screen to the right, while the right-handed option will rotate the screen to the left.

Controls

 * / (left/right): Move capsule
 * / (down): Drop capsule
 * / (up): Quick drop capsule (requires enabling Quick Drop in options to do so)
 * / / : Rotates capsule clockwise
 * / / : Rotates capsule counterclockwise
 * In Virus Buster, rotate Gamepad display
 * / : Pause game, and display pause menu

Reception
Overall, Dr. Luigi received average scores from critics, having a Metacritic score of 65/100 based on 38 reviews.

Trivia

 * Some of the music tracks are reused from Dr. Mario Online Rx.
 * Even though several games were released during the Year of Luigi, this is the only game that acknowledges the event. As an example, the official label is found on the pedestal that Dr. Luigi stands on during gameplay.
 * Upon beating levels 5, 10, 15, or 20, Dr. Luigi and the Viruses will do different things depending on which level is played and which speed it is played on.