101 Pikmin challenge
A 101 Pikmin challenge is a challenge run where a player collects all treasures in Pikmin 2 using only 101 Pikmin, the known minimum amount possible. This challenge contains no deaths, and uses Candypop Buds to switch Pikmin types when necessary. 100 Purple Pikmin are needed to lift the Doomsday Apparatus, plus one Red Pikmin, to avoid an extinction. Unlike the previous known minimum of 103, there is no need for one Yellow or Blue Pikmin because their Onions are never considered "discovered", although those Pikmin types are still obtained. This challenge can be completed in 8 days.
103 Pikmin is the minimum number of Pikmin possible in a run that does not use any exploits. To simply repay the debt, 35 Pikmin is the minimum amount, given that it is possible to obtain money repeatedly from enemies defeated in caves, but in order to reach the first cave, 35 Pikmin are needed for the paper bag at the Valley of Repose.
Normally, 103 Pikmin would be the minimum required amount. It is mandatory to grow 35 Pikmin in order to continue with the second day, since there is a paper bag on the Valley of Repose that requires the weight of 35 Red Pikmin (the only available type at the time) before even the Emergence Cave can be discovered. From there, the player may use Candypop Buds from various caves to change Pikmin types when needed. The task that requires the most amount of Pikmin is 100 Purple Pikmin, which are needed to carry the Doomsday Apparatus, meaning a total of 100 Pikmin is the minimum necessary, task-wise. By the time that treasure can be collected, Red, Yellow, and Blue Pikmin are already part of the player's arsenal, but because one cannot convert all Reds, Yellows, and Blues into Purples, since doing so would trigger a Pikmin extinction, at least one of each of those three types must be alive, raising the total minimum to 103 (100 Purples + 3 of each basic color).
However, the Pikmin extinction will only take effect if the respective type's Onion has been considered "discovered" by the game. If it hasn't, the Pikmin count for that type can reach 0 and no extinction will take place. The only way to do this is and still be able to use that Pikmin type is to convince the wild Pikmin to join Captain Olimar's side without interfering with the Onions. This is only possible for the Yellow and Blue Pikmin, since Reds are obligatorily obtained the "proper" way on the first day. To do this, the player must use exploits to get to the wild Pikmin without triggering the usual discovery cutscenes, and then using the leaders and Pikmin at their disposal to drag an idle wild Pikmin towards a patch of nectar weed, since wild Pikmin cannot be called to the group but can be pushed around. Once near, the Pikmin will begin working on the nectar weed, and at this point, the Pikmin still can't be used, but if it finishes the task, the game will change its status from "wild idle" to "friendly idle", meaning it can now be used by the leaders.
Still, it will be impossible to grow any more Pikmin of that type until that species is considered "discovered" by the game. This can happen when the first Pikmin seed of that type is plucked, meaning that a Swooping Snitchbug or Mamuta can be used to bury the lone Pikmin so that a leader may then pluck it out. From there on out, it is possible to use Yellow and Blue Pikmin like normal, but their Onion will never be considered "discovered" by the game, which will stop the Pikmin extinction checks from happening.
8 day run outline
The following is a brief outline of what needs to be done for an 8 day run, skipping day 1, which plays the same as any normal run.
Pikmin count: 30 Reds, 29 Purples, 0 Whites, 0 Yellows, 0 Blues (59 in total).
Pikmin count: 1 Red, 0 Purples, 58 Whites, 0 Yellows, 0 Blues (59 in total).
Pikmin count: 1 Red, 0 Purples, 4 White, 95 Yellows, 0 Blues (100 in total).
Pikmin count: 1 Red, 10 Purples, 34 Whites, 25 Yellows, 31 Blues (101 in total).
Pikmin count: 1 Red, 50 Purples, 3 Whites, 17 Yellows, 30 Blues (101 in total).
Pikmin count: 1 Red, 70 Purples, 1 White, 19 Yellows, 10 Blues (101 in total).
Pikmin count: 1 Red, 100 Purples, 0 Whites, 0 Yellows, 0 Blues (101 in total).