All items that are being expanded and fine-tuned for posting go to the top, unpolished ideas settle to the bottom or get deleted for reason of fail.
A swimming pool that lets you walk on water. Or a lake/pond? Maybe only organic things float and nonorganic things sink. Removing water with a plastic bucket is possible; the moment the water leaves the pool/lake it behaves like normal water. Rainfall or humans introducing "new" water cause no apparent change to the effects.
Feh. Feels bland still, unless: If the surface is treated as solid and impermeable, would splashes/waves be sharp and jagged? Most likely would cut your feet to ribbons.
Vampire squash. …seriously. The actual tale doesn't seem to have them do much, though, aside from roll around and growl. There's already the bad joke tomatoes… Maybe they just turn into soggy bleeding bags of meat. That roll around and growl.
Rather than wires (SCP-217) or tentacles (SCP-486), or a paranoia fuel that makes you scratch your skin off, your flesh starts to turn into synthetic fibre; organs into acrylic stuffing, etc. End result: Human turned into a rag doll.
Disembodied Audience. Idea brought up in chat. Invisible, intangible voices that haunt Site-19. When "victorious" or otherwise notable incidents occur, it bursts into applause. Other vocalizations include laughter (personnel tells a joke, or something slapstick occurs) or "Aw…" noises at cute moments. The voices do not respond to questions or statements. They occasionally tag along behind a person they find entertaining, but "get bored" and find someone else.
The Repository of Lost Toys. Came up in the DnD mundi roleplay. A place, room, closet, box, or similar that spawns a toy, security blanket item, or similar from your childhood, long forgotten. Consider odd things that come up for some of the staff. Get one of the humanoid SCPs to open it and see what comes out.
La Llorona. Based on the Myths Over Miami article. Unsure what angle to take with this one.