A very good friend of mine had four of the Ribbon Plants in her aquarium. After several months, the plants had used up their stored energy and could no longer live underwater. They began to lose color, got soft and mushy, and decayed. She had a bad ammonia spike as this happened but luckily knew enough to recognize it and did large water changes. She removed the plants and threw them away in the trash.
The next morning, she found her older cat dead in her kitchen. The dog she had was also poisoned but still alive. She took the dead cat, her other cat that seemed ok and the dog to the vet. Several hundred dollars later, and 2 days hospitalized, the dog recovered. The necropsy of the dead cat showed the same toxic ingestion. The other cat did not eat the plant at all, so did not get sick.
Kiara1125, I don't know how long you've had the Ribbon Plant underwater, but it (they?) will eventually die and decay. I only mentioned that the plant was toxic to dogs and cats because I've read your posts and you've mentioned having them.