There are four secret bosses hidden around the map, one in each Clan territory. Each one guards a corner of the map, and each has a different attack style. If you match your damage type to their weakness, the fights go much smoother. Here is where to find all four.
Overview
Each secret boss sits in a different corner of the map and belongs to a different Clan. Their attack styles vary, so you need to switch up your damage focus for each one. Below is the quick breakdown, then the details.
| Boss | Location | Clan Territory | Attack Style | Damage to Prioritize |
|---|---|---|---|---|
| Badger | Top left corner | ShadowClan | Mostly defensive attacks | High trick damage |
| Fox | Top right corner | ThunderClan | Mostly trick attacks | High sharp damage |
| Snake | Bottom right corner | WindClan | Mostly sharp attacks | High defensive damage |
| Dog | Bottom left corner | RiverClan | Mostly sharp attacks | High defensive damage |
First Boss: Badger in ShadowClan Territory
Head to the top left corner of the map, into ShadowClan territory. You will find a badger there. It leans on defensive attacks, so bring high trick damage to break through. I found the trick stat easy to overlook, so check your build before you walk in.

Second Boss: Fox in ThunderClan Territory
The second one is in the top right corner, in ThunderClan territory. This is a fox, and it mostly uses trick attacks. Stack high sharp damage for this fight. Watch your own defenses here, since the fox hits with trick.

Third Boss: Snake in WindClan Territory
Go to the bottom right corner, into WindClan territory. A snake waits there, and it attacks with sharp damage. Prioritize high defensive damage so you can take those hits. This one caught me off guard the first time because I was set up for the wrong damage type.

Fourth Boss: Dog in RiverClan Territory
The last one is in the bottom left corner, in RiverClan territory. It is a dog, and like the snake it uses mostly sharp attacks, so high defensive damage works here too. This is the hardest of the four. If you are not max level, clear the other three first to gain experience before you challenge the dog. I suggest saving this one for last.

Conclusion
Four corners, four Clans, four bosses. Match your damage to each one and the fights get much easier. Take your time with the dog in RiverClan, and level up on the others first if you need to.