The Bad Future that is created by Doris. There's no soft colors anywhere, only red, black and green, and humans are Brainwashed slaves that look like zombies - including the Robinsons, who come after Lewis and try to shove him and the time machine over a cliff.
Bowler Hat Guy's death in the Bad Future; he's seen panicking and desperately declaring that all he wanted was to ruin Lewis' future and not the massive scale apocalypse he's witnessing. He is promptly mobbed and presumably torn apart offscreen by Dor-15's clones.
Wilbur disappearing in front of Lewis when the Ripple Effect catches up to him. The sky is stormy, the wind is roaring all around them as Wilbur is trying to give him a peptalk. Then wisps begin to come off his body. Wilbur feels his chest as he begins to realize what's happening and says, "Lewis...? Leeewwwiss!" as he vanishes into the sky in a swirl of smoke.
Considering the fact that when Doris is also removed from existence in this manner, she is ripped apart piece by piece, imagine how painful that must've been for Wilbur.
Mr Harrison's allergic reaction to being sprayed with peanut butter near the beginning is a bit creepy, because of how swelled he gets.