Challenges are a feature of Pikmin Bloom, unlocked at level 15. Mushrooms of various colors and sizes appear around the world, and the player can send a group of Pikmin to attack them. Multiple players can join in, and participants will receive fruit as a reward, and a score that measures how well the participants did.
The amount of Pikmin that can be sent on a challenge by a player will increase over time based on the player's level, starting at 10 Pikmin. The challenge selection screen lets the player choose which Pikmin to send, and the strength value of the selected Pikmin can be seen in the top left corner. The higher the strength, the more efficient the Pikmin will be at completing the challenge.
Only three challenges can be done by a player in a day. Up to five people are able to join in on a single challenge.
Mushrooms are the objects destroyed in challenges. Like big flowers, they grow at points of interest in the real world. A challenge can only be started if its mushroom is close enough to the player. After the challenge is complete, the mushroom is destroyed, and grows back in the same location a few minutes later, without any input. The mushroom type that grows is randomized, but there seems to be a system where some mushrooms are removed from the selection if no players nearby have access to the corresponding Pikmin type.
Mushrooms come in various forms that differ in size and color. The hierarchy of the sizes are small, normal, large, and giant, with each size increasing in health. The larger the mushroom, the bigger the reward for destroying it. Some mushrooms have more or less health than other colors of the same size, such as gray or white mushrooms, being tied to the preferred Pikmin's attack power. The color of mushrooms can also determine the type of nectar players get as a reward (e.g. blue mushrooms give blue nectar, red mushrooms give red nectar).
When the player is selecting Pikmin for the challenge, a power value appears in the top left corner of the screen. This shows how strong the selected squad is against that mushroom. Adding a Pikmin will increase the value by some amount. The amount depends on the type of Pikmin, its friendship, its maturity, whether it is a Decor Pikmin, and the color of the mushroom being attacked.
Red Pikmin, Yellow Pikmin, and Blue Pikmin (the main types) all have the same attack power values. A leaf Pikmin with 0 hearts of friendship has a power of 4, and a flower Pikmin with 3 hearts of friendship has a power of 11. Purple Pikmin and Rock Pikmin are stronger than the main types: a leaf Pikmin with 0 hearts of friendship has a power of 5, and a flower Pikmin with 3 hearts of friendship has a power of 13. White Pikmin and Winged Pikmin are weaker than the main types: A leaf Pikmin with 0 hearts of friendship has a power of 3, and a flower Pikmin with 3 hearts of friendship has a power of 9.
If a Pikmin is a Decor Pikmin, an extra 4 points will be added to its power. If it is attacking a mushroom of the same color, the power will be roughly doubled. Note that while the number displayed is an integer, attack powers are not integers. It is not known exactly how attack power works.
Once the Pikmin are sent on the challenge, they rush towards the mushrooms and start attacking them. Most types latch on to a mushroom and start attacking it at a constant rate, with each attack doing a small amount of damage. From time to time, they get off the mushroom, walk back to their starting position, and walk back to the mushroom to start attacking again. Each hit decreases the health of the mushrooms, and at certain points, one of the mushrooms in the group will collapse, leaving the Pikmin attacking it to start attacking the main one.
Although damage is presented as something dealt by each individual attack, the rate of damage is actually predetermined by the attack power of the Pikmin selected for the challenge. Each Pikmin hit does as much damage as it needs to to keep the health of the mushrooms in line with what is should be given how much time has passed and what Pikmin are attacking it. The amount of time it takes to destroy all mushrooms (in seconds) is equal to the health of the mushrooms, divided by the total attack power of the Pikmin on the challenge, multiplied by 4. For example, a normal-size mushroom with 21,000 health, attacked by a group of Pikmin with 200 attack power, should take 420 seconds or 7 minutes to destroy.
Once the challenge is complete, the player is provided with their score and an amount of stars, followed by the Pikmin bringing the certificate of their challenge and a small number of shiny fruits to be given to the player, providing them with regular or pansy nectar of a specific color. Friendship is also awarded after challenges.