Unions can be formed in the library. They are activated by inserting all of the required heroes into each slot on the union page.
You can use heroes that you own and ones that are owned by people on your friends list.
That’s one of the many reasons as to why you should max out your friends list ASAP with active players.
List of Unions
There’s 3 different buffs you can acquire from each union. The first buff just requires 3 of those heroes. The 2nd one requires 3 of those heroes in Epic+ rarity and the 3rd one requires all of those heroes in Legendary+ rarity.
These buffs apply additional attributes to all heroes in that specific union.
They’re not permanent, if the union is broken because a friend was removed etc, you’ll lose them.
How Do The Union Buffs Work?
There might be a bit of confusion as to when the buffs apply.
Once the buffs are activated, all heroes that you own of that union will passively receive them.
The rarity of the heroes you own does not need to match the buffs. It applies to all heroes, regardless of their quality.
They don’t need to be in the same team to receive the buffs either, each individual hero of the union will have the additional attributes at all times until it is deactivated.