If you are losing all of your battery life and you want to play but still conserve it, this is one of the few games in existence with a backup battery saving option. Go to the options menu. Then, find the shadows and turn them off, and find battery saving mode and turn that on too. This decreases the frame rate from 60 to 30 causing you to use a whole lot less battery life.
If you want to unlock the first secret character, look for the Hipster Whale mascot to be floating around in the river, then jump on it as you would a log. Do this and then finish the stage or just jump into the water right away. When you finish, you will have unlocked the Hipster Whale.
If you want to unlock the first secret character, do the following. Play as the Festive Chicken and keep going until you see a clearing with a Christmas tree in it. Once you see it, go inside and start trying to catch one of the gifts. Then leave and finish out the stage as usual. Once you are done with the stage you will unlock Gifty, the hopping Christmas present.
Many of the characters in this game turn it dark, allowing you to simulate playing at night. The Vampire, Zombie, Gravedigger and Wolf are examples of these. They all do it a little bit different. The Gravedigger has horrible visibility, and ghosts appear. The Vampire turns into a bat, then into a humanoid, then bats fly overhead, and then repeats. The Zombie makes a different color palette appear compared to the other nights (more yellowish).
One of the main unexpected obstacles to watch out for is the police squad car. Look for the blue and red flashing lights to appear (not the red ones only as that is obviously a train). Give it about a second and then the squad car will roll by at high speed. If you have your sound on you will be able to hear a siren as a warning, too.
Doge is one of the funniest yet most annoying unlocks, as he will cause Comic Sans text from the meme to float around on the screen and get in your way. Frankenstein will go black and white like the movie and shoot lightning. The mad wizard will shoot lightning at trees but with none of that black and white stuff.