In this challenge, you must do objectives without being seen. If you get seen 5 times, you need to start over. there's an achievement/trophy called "Truely Invisible" that can be earned by completing the challenge without being seen once.
Use sounds to distract bears to something else away from your objective.
Don't get seen and stay close to the woods.
You can still use noise (Scare, gunfire) to gather the bears together. Just make sure you're in the woods or hidden by a wall.
Use clothes with you can walk around without being seen.
Attack from behind or a distance.
Try using a costume with a long ranged weapon (Oozy, Revolver,etc.) while hiding in the woods.
The only invisible challenges in the game exclusively feature bears that can't see you in the woods.
Try setting a few traps in front of a central section of woods at the start of the challenge. From there you can use the Scare to attract all the bears so they can get trapped/witness traps.
Remember you can not use Super Kills or Super Scares on this mission. If their head turns toward you, it still counts as being seen.
Most object kills don't count against you, since you generally shove the victims into something from behind.