Cookies as playable units can be upgraded and leveled in a variety of ways.
Leveling Up and Star Jellies
Leveling up is the most effective method of increasing a Cookie's Power Level, improving their overall effectiveness in combat gameplay.
For a Cookie to level up, they must gain Experience Points. While most modes will grant a small amount of these, the most efficient method of leveling up a Cookie is through feeding them EXP Star Jellies. Cookie Houses are the most reliable source of EXP Star Jellies for a player, altough almost every feature and game mode will also reward them" the Fountain of Abundance, World Exploration, the Tower of Sweet Chaos, Kingdom Pass Landmarks, shops such as the Medal Shop or Mileage Exchange, and more.
The amount of Experience Points given by a Star Jelly depends on the Jelly's Level, with these levels ranging from 1 to 8, and their respective given Experience increasing exponentially at higher levels. However, as a Cookie's Level raises higher, the required Experience Points to gain more levels increases as well. Thus, increasing a Cookie's Level becomes more difficult at higher levels, plateauing at levels 50-60.
At launch, the maximum Level any Cookie could reach was Level 50, but this has since been raised to Level 60.
Level Up Table
If a full Cookie has not been pulled, collecting at least 20 of the Cookie's Soulstones will allow them to be unlocked immediately as if being drawn from a Gacha. Conversely, drawing a duplicate Cookie will instead give the player 20 of the Cookie's Soulstones as compensation. Finally, if a Cookie is fully promoted to 5 stars, drawing them or their Soulstones will instead give the player Mileage Points, with the exact value of points per Soulstone varying depending on the Cookie's Rarity.
The promotion of Cookies requires progressively more Soulstones with each Rank. 290 Soulstones total are required to promote a Cookie through every Rank.
Skills and Skill Powder
A Cookie's Skill is their unique special combat ability—specifically, an action that can only be performed when its cooldown is cleared. Skills range in utility from being offensive to defensive, as many Skills have effects such as healing, Buffs for teammates, Debuffs for enemies, and so on.
A Cookie's Skill has its own dedicated Level, requiring Coins and Skill Powder to raise. Raising this Skill Level increases the effectiveness of the Skill by improving one or more of its specific numerical stats. However, a Cookie's Skill Level value cannot exceed their Cookie Level value; thus, a Cookie's Level has to be increased before its Skill Level can also be increased. (For example, if a Cookie's Level is Lv. 10, then their Skill Level can only be raised up to Lv. 10.)
The amount of Skill Powder needed to enhance a Skill Level depends on both the current Skill Level and the Class of the Cookie. Skill Levels 1-20 require standard Powder, 21-40 require Refined Powder, and 41-60 require Pristine Powder. The Powder must match the Class of the chosen Cookie, with each Class having their own varieties of standard, Refined, and Pristine Powder. For instance, if one were to increase the Skill Level of Rye Cookie, a Ranged Cookie, from Lv.29 to Lv.30, they they would need 5 Refined Ranged Powder and 7,400 Coins.
The most efficient way to acquire Skill Powder is through completing Today's Bounties. Skill Powder can also be acquired from the Medal Shop, Trading Port/Seaside Market, Rainbow Shell Gallery, and specific World Exploration stages.