Extensive Nightfall guide

So, here's a Shadow guide, to steal some (spot)light from the legends :P.

Best fun to have as a Shadow is at the beginning of the match, so look for a fast way to die. If you don't care about doing stuff as a legend, you can kill yourself very fast by dropping from the ship right into the water at the nearest edge of the map. This way, you come back as a shadow very quickly, being able to see where most of the other players are landing and even catch some of them right as they set foot in Kings Canyon. Then, the most hilarious part begins: some don't even know you're right behind them and keep looting like, some get really scared and run out in the open as if you wouldn't catch them, some duck in corners thinking that you won't see them, some surrender and start dropping loot or weapons in hope that you'll spare their life. This way, you can easily do about 3-4 legend kills before dying.

Next, chase legends fighting each other, to third party them. Jump on them as they reload or heal for an easy kill. If you get eliminated, go back to the same location, you'll probably get one of them eventually.

As more shadows join the match, look for where they land and try to group up with them. Tease encountered legends a little, some of them will try to shoot you and get noticed or flanked by other shadows.

Once the evac ship is coming, start checking buildings around the landing zone for campers. verify each roof, Pahtfinders often sit their waiting for the right moment to pop a zipline for the win. In some cases, it's even possible to land on top of the ship when it arrives and, from there, you can jump on any zipline and down incoming players.

Doing all of the above increase the chances of winning as a shadow and also becoming a champion, if you manage to get 5-6 kills. Also, since your shadow has the same shape as your chosen legend, it's possible that they use the same hitbox, so make sure you pick a smaller legend, its shadow may survive more bullets.