In Dota Underlords you can upgrade up your units by combining them. These units will progress in rank throughout the match, but you can also combine them to upgrade quickly. To combine units in Dota Underworlds you simply need to purchase three of the same units. After you have two units of the same type (and rank), the next unit that you purchase will combine with the others to be a more powerful version.
Three of the same units with the same rank will automatically combine to a more powerful version
As you can see in the image above we have two Shadow Shaman characters on the board, with a third Shadow Shaman available for purchase in between rounds. Purchasing this Shadow Shaman will turn these three units into one, more powerful two-star Shadow Shaman.
Get more units by purchasing them between rounds
As we progress through the Underlords match we will have another opportunity to purchase more Shadow Shaman characters. Say we wanted to get two 2-Star Shadow Shaman. We would need to purchase three more Shadow Shaman from the shop between matches.
This process than can then be repeated to get a three-star character as well, but you will need even more characters of the same type. We are then going to combine three 2-star Shadow Shaman to make one 3-star character. Regardless of whether you are trying to combine one-star characters, two-star characters, or other you will notice that the next character you are going to purchase will automatically change to the more powerful version and will have a glowing orange aura over them. In some instances this can greatly decrease your available characters to fight with in a specific round so act accordingly.
Combining characters is a great way to make your team more powerful in Dota Underlords, but simply going for a multi-star unit can leave you depleted of gold and available units as you’ll likely need to spend gold to roll new available units each round, instead of spending it on units that you can use in the current fight.