When the player collects enough experience, they will gain a level up. Each successive level up requires more experience than the previous. Upon level up the game is paused and the player is given 3 or 4 unique options consisting of weapons and passive items to choose from. If the player chooses an item they do not have, it will be added to their inventory. If they already have the chosen item, the item will be upgraded to next level. After selecting your item the game resumes and the character gains a brief moment of invulnerability.
The player cannot be offered new items if the already have 6 different items of that type. Similarly, if an item is at maximum level, it also cannot be offered to the player. When both of these conditions are met and player has nothing left to upgrade, level ups will instead grant the options to gain extra Gold or restore health with Floor Chicken. Alternatively, if a player has nothing left to upgrade but Limit Breaking is active, level ups will then offer extra levels to already maxed weapons.
If the player has invested in the Skip or Reroll PowerUps, they will also have the options to skip the item selection for some experience or gain a new set of items. Skip and Reroll are not available when the player has maxed out their inventory.
Player starts at level 1 and has to collect 5 XP to level up to level 2. Thereafter, the requirement increases by 10 XP each level until level 20 (i.e. 15 XP is required to go from level 2 to 3, 25 XP from 3 to 4 and so on). From level 21 to 40 the requirement increases by 13 XP each level, and from level 41 onwards the requirement increases by 16 XP each level.
Additionally, at levels 20 and 40 an additional amount of XP - 600 and 2400 respectively - is required to level up to the next level. However, at these levels the player also gains +100% Growth, increasing their experience gain, until they reach the next level.
Random selection of items
Each item in the item pool has weight that is specified by their rarity value. The weight of the whole item pool is the sum of the rarity values of eligible items. Three (or four) items are then selected from the pool at random without repetitions (i.e. an item cannot be offered more than once per level up). The rough probability of an option to be a certain item is:
Currently, the total weight of the weapon pool is 1,473 and the passive item pool is 1,250 (total 2,592). Rough probabilities of receiving a certain item of a rarity value can be found in the table below.
Receiving owned items
If the player's inventory is not full, there is first an attempt to specifically offer items already owned by the player. The chance to be offered items already in your inventory is affected by Luck and can be calculated as:
where x=2 if the player's level is even and x=1 if the level is odd.
The check is performed twice and, if successful, an item already owned by the player will be randomly selected to appear as an option for each successful check. However, if the second roll selects the same item as the first it is discarded and a new item is pulled from the pool of all items, as the same item is not be offered more than once in the same level up.
It is possible to sometimes gain four item choices upon leveling up. This depends on the character's Luck. The chance to receive a fourth option is: