some typos. Also, Tantabus doesn't make Luna go evil. The whole point is, she created it to "scare herself straight" by making her relive the nightmare of her evil - but as the Tantabus grew in strength, it started to become evil in her stead. - she was good and horrified by what she had done, while the Tantabus grew stronger for her guilt.
You asked about poison joke. Not sure if it should be an item or an encounter card. The plant grows in everfree forest, in large patches, and the effects strike any creature that touches them - it takes some time to set it, usually becoming apparent by the next morning.
The poison joke curse takes form of a 'humorous' polymorph effect. It is never dangerous by itself, but may leave the victim defenseless against other hazards.
The effects we have seen in the series:
Twilight - horn becomes floppy and useless
Rarity - fur becomes a mess of shaggy hair
Pinkie Pie - swollen tongue, making her unable to speak properly
Rainbow Dash - wings switch sides (turning them upside down)
Applejack - shrunk 3 size categories
Fluttershy - speaking with a deep male voice.
The effect can be cured with herbal remedies.
