A life-threatening prank would be appropriate for Undyne. There's no fun and games until somebody's gettin' hurt, or something like that. Hearing "April fools!" again after having it repeatedly played during the stream has left me with a bit of a headache, but I'll get over it after a while. My only complaint was the sudden transition from lying on the floor to running for his/her life. It would have made more sense to call while Frisk was wandering about outside and having spears suddenly flying towards at her/him a moment after she delivers the punchline.
I was happy to join, and will do so again when I don't have to work, but I still won't comment during the streams... probably. And thank you for continuing to share your stuff with Newgrounds, Seven... even the ones made for Twitter.