This list will probably be dominated by Wii>Wii U or DS>3DS series.  Wii ___, Brain Training, Nintendogs, etc.

These two won't make it into a list of largest drops, but they are somewhat notable for seeing large declines despite going from one to multiple platforms.  Epic Mickey and de Blob.

Lol...

Why do you compare 7 years of sales with 10 months sales?Wouldn't be right to compare them in the same time frame?Are you bored of doing it?This comparison makes things to seem worse than they really are...

MK8 has like a million more sales than on VGC and hasn't stopped selling (I wouldn't be surprised if it reaches 10m). I'd say it at least has a predictable drop considering install base.

Wii Sports Club is probably it, though it's an unfair comparison, as the main volume of it's sales is the individual passes for each sport. We don't know how well that goes. Otherwise it's probably Wii Fit.

I have to say that I hate comparisons that include wii and ds,because it's like apples and oranges(the reason why is self-evident) and of course not because it doesn't fits my boat as a malignant person would say...I'm very satisfied with the fact that is outpacing Mario kart double dash,and that it seems to be capable of surpassing super mario kart/mario kart 64!Comparison are usually made with things that have some similarities and not when they are completely different...
The title isn't accurate,it should be:Biggest drop of game,from predecessor to successor!Not biggest drop in a games series,I have said upper why...
Mario kart 8 is the successor of Mario kart wii,and you called it game series...lol Mario kart plain,is a game series.

Here are a few dramatic examples that I know of. Note that in some cases, the latest games are still selling at least a bit, especially since most examples are fairly recent. This also means plenty of Nintendo-related examples.

Nintendo Exclusives

• Wii Fit - Fell from 21.74 million sales for Wii Fit Plus to 0.58 million for Wii Fit U. This is a sales drop of over 97%.
• Wii Play - Fell from 28.89 million for the original to 0.91 million for Wii Play: Motion. This is a drop of over 96%.
• Mario & Sonic Olympics - The 2012 console version sold 3.69 million, compared to 2014's 0.57 million. This is a drop of about 85%.
• Nintendogs - The DS original sold 24.66 million to the 3DS sequel's 3.54 million. This is a drop of over 85%.
• Super Monkey Ball - The Wii launch title Banana Blitz sold 2.23 million, while its successor, Step & Roll, sold 0.39 million. This is a drop of over 82%.
• Mario Party - The Wii iterations, 8 and 9, sold 8.20 million and 3.01 million, a decrease of about 65%.
• Cooking Mama - The second, third, and fourth games sold 3.58 million, 1.67 million, and 0.58 million respectively. Those are declines of about 53% and 65%.
• Professor Layton - The series plummeted on the 3DS from 2.63 million for Last Specter to 1.58 million for Mask of Miracle to 0.76 million for Legacy of Civilization. Those are drops of 40% and 52%.
• Zelda - Depending on whether one includes GameCube sales, Twilight Princess sold 7.09 million or 8.69 million. Skyward Sword sold 3.90 million, which can either be seen as a 45% decline or a 55% decline.

PlayStation Exclusive

• God of War - On the PS3, God of War 3 sold 4.77 million compared to Ascension's 2.11 million. This is a drop of over 55%. On the PSP, Chains of Olympus sold 3.16 million compared to Ghost of Sparta's 0.96 million. That is a 70% decline.
• Gran Turismo - The main PS3 entries, 5 and 6, sold 10.59 million and 3.10 million, making a decline of about 70%.
• Dissidia - The first of these Final Fantasy spinoffs for the PSP sold 2.21 million. The second sold 0.85 million, a decline of over 61%.
• LittleBigPlanet - The PSP version sold 2.51 million, compared to 1.09 million for the Vita version. That is a 57% decline
• Sly Cooper - The second PS2 game sold 1.81 million, compared to the third's 0.83 million. A decline of 54%
• Resistance - The PS3 trilogy sold 4.29 million, 2.44 million, and 1.45 million copies each. Those are declines of 43% and 41%.

Xbox Exclusive

• Gears of War - The third game sold 6.14 million compared to Judgement's 1.53 million. This is a 75% drop.
• Kinect Sports - The first and second games sold 6.06 million and 2.29 million copies, a decline of 62%.
• Dance Central - The second and third entries sold 2.01 million and 0.79 million copies, a decline of 61%.
• Forza - Numbers 4 and 5 sold 4.45 million and 1.95 million respectively, a drop of 56%.

Multiplatform

• Kung Fu Panda - The 2008 movie tie-in sold about 6.37 million across platforms, thanks to bundling with the 360. Kung Fu Panda 2, released in 2011, sold about 0.67 million, a drop of 89%.
• Castlevania: Lords of Shadow - The 2010 original sold 1.71 million. The second, released in 2014, sold 0.34 million. This is a decline of 80%.
• Dead Island - The original sold 4.72 million. Riptide sold 1.43 million. A 70% decline.
• Star Wars: Force Unleashed - The original sold 9.85 million. The second sold 3.76 million. A Decline of 62%.
• Devil May Cry - Devil May Cry 4 sold 2.91 million copies, compared to DmC's 1.19 million. The drop is 59%.
• Soul Calibur - The fourth game, released in 2008, sold 3.01 million copies. SCV sold 1.28 million copies. The decline was 57%.
• Guitar Hero - GH3 sold 16.29 million, World Tour sold 9.96 million, Guitar Hero 5 sold 4.85 million, and Warriors of Rock sold 2.58 million. That's roughly a 54% drop every year. In comparison, Rock Band fell less quickly.Batman Arkham - Arkham City sold a total of 10.63 million. Arkham Origins sold 4.40 million, about 41% of its predecessor.
• Medal of Honor - The 2010 version sold 5.82 million copies. Warfighter sold 2.85 million, a decline of 51%.

Note: Sports series like Konami's Winning Eleven and EA'sPGA Tour, and NBA Live series have all seen notable declines as of late.

That's all I have at the moment.

But Wii Sports Club is a remake...

New Super Mario Bros. (Wii --> Wii U. DS --> 3DS)

Almost all of Nintendo franchises

Actually Mario Kart 8 is performing better than Mario Kart Wii if look user base, on other hand Wii Sports have biggest drop but again Wii U version is just HD port.

I dont think its fair at all to compare sales of games from best selling Nintendo console ever with probably worst selling Nintendo console ever.

The king of this list is definitely Wii Sports to Wii Sports Club XD It'll be a while till we see a drop off quite like that again