These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Demonic Spiders: In Columns II, some blocks will turn into skull blocks. Clearing out a skull block will cause the bottom of the playfield to rise up by a few cells.
Older Than They Think: If you're familiar with the series' more intricate physics, you'll notice that some of themnote in particular, the delay between a piece hitting the floor and it locking, fast sideways movement, and the delay between piece lock and the next piece are taken out of Sega's 1988 Tetris game.