My favorite pranks to pull on people are:
Slap cam. And I don't just tap people on the face, I go in for a proper whack. Whether its with my hand, a pillow, or my hand with shaving cream/toothpaste on it.
A rubber snake tied to the inside of the trash can lid.
Replace an egg in the egg box with a rubber one. You can just leave it there and wait for someone to mistake it for a real one, or drop it on the floor in front of someone else so they think it's gonna smash.
Mix up all the gross smelling things you can find in your kitchen in a bowl and dump it all over someone who's in the shower. Especially if you know they just washed their hair. They'll have to do that all over again. I know this one works because Mani and I did it to Camila.
Clingfilm over the toilet bowl. You won't actually see how this one works out but trust me, you'll hear it.
I've done those ones several times but the one I only did once was the Weeping Angel prank. I got the inspiration for it on YouTube. We were on tour, in a hotel, and I asked the crew, after watching the video, if I could have a cardboard cutout Weeping Angel. I can pretty much have whatever I want, within reason, a privilege I don't exercise that often because I'm not a spoiled demanding brat, but I did this time.
When I got it, I had to choose a victim. When we're in hotels, we have three rooms between us. Normani shares with Lauren, I share with Camila and Ally has her own room, but if Camila starts snoring I go into one of the other rooms. Anyway. I picked Ally in the end, and I hid the cardboard angel in her shower and ran back to my room.
I waited patiently for her to get back, she went out somewhere, and I knew she'd be showering. I heard her open the door to her bathroom and pull the shower curtain back, and then, the loudest scream I've ever heard in my life! followed by Camila and Mani shrieking and Lauren swearing from her and Mani's room. They all went in there to see what happened and I did too, and Ally figured out I did it pretty quickly. She made me sleep in her room that night because she was freaked, and she slept in my bed.