Biggest drop in sales in a game series?

[Kresnik]

Brain Training

1	Brain Age: Train Your Brain in Minutes a Day	DS	2005	Misc	Nintendo	4.74	9.18	4.16	2.04	20.12
2	Brain Age 2: More Training in Minutes a Day	DS	2005	Misc	Nintendo	3.43	5.36	5.32	1.18	15.29
3	Brain Age: Concentration Training	3DS	2012	Puzzle	Nintendo	0.06	0.00	0.00	0.00	0.06