> For the complete documentation index, see [llms.txt](https://docs.evermoon.games/evermoon/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.evermoon.games/evermoon/evermoon-economy/defi/building-challenge.md).

# Building Challenge

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The Building Challenge is a unique feature that gives players the opportunity to upgrade their lower-tier NFTs, including heroes, skins, and runes, into higher-tier ones. This process involves combining multiple NFTs of the same type, along with the payment of a certain fee in $ES, the secondary token. The precise quantity of NFTs and the fees required for a building challenge depend on the type of NFT involved.

## Heroes&#x20;

When players use heroes for the building challenge, they must combine 6 NFT heroes along with a combining fee of [$ES](/evermoon/evermoon-economy/tokenomics/everstone-token-usdes.md) . The reward for this challenge will be 1 random rare NFT skin.

## Skins&#x20;

If skins are used for the challenge, the players must combine 6 NFT skins of the same rarity. The $ES fee for combining depends on the rarity of the skins used. The reward will be 1 random NFT skin of a higher rarity.

## Runes&#x20;

Much like the skins challenge, when players use runes for the building challenge, they must combine 6 NFT runes of the same level. The combining fee in $ES depends on the level of the runes used. The reward will be 1 random NFT rune of a higher level.