The duplicates are then fed to an item

This doesn't just show in the use of currency paid to obtain items such as gacha, but also in D2R Items mechanics, as well as the information about drop rates in the more scarce items. Gacha is the practice of using game currency, whether it was free or purchased through an in-game shop in order to get something you want like pieces of equipment in the case of Dissidia Final Fantasy Opera Omnia or characters from the ever popular (and ever-lasting) Fate/Grand Order or Genshin Impact.

In Diablo Immortal's case, they use Legendary Crests (which can be bought or earned) to increase the odds of a five-star gem showing up in the dungeons and dungeons endgame. While not entirely conventional in its presentation (most gachas are played out by "rolling" on a time-limited banner) it is still engaging with the kind of randomness in a similar manner. In many ways this is how it's like the Diablo game has been working towards these mechanisms since its beginnings, according to a piece Maddy Myers wrote a few weeks in the past.

Diablo Immortal also, in simple terms, draws direct inspiration from an "feeding" technique that a lot of Japanese, Korean, and Chinese mobile games have normalized for more than 10 years. "Feeding" entails raising the stats, attributes, or rarity of an item , by getting a duplicate of a drop. The duplicates are then fed to an item of similar rarity, which increases the overall stats for the item. Generally five copies are needed in order to max out a character or item.

My first introduction to "feeding" was through Fate/Grand Order, which was originally published to Japan in July of 2015 and made a profit of $4 billion dollars across the globe in 2019. To Diablo 2 Resurrected buy items create a character that was the best possible I had to purchase copies of each.