Disco Ball, added in Beta 13.4, was card 3/9 of the 15 revealed on Twitter. It didn't get any changes when it was released. Previous Versions can be found here.
Disco Ball allows you to transform all spells in your hand into other random spells and let their cost drop by 1.
This can be useful with C-Round (in case it dies multiple times) or against Rouxls Kaard to turn "useless" spells into new, more usable spells.
Best used in a Perseverance deck due to all its spells (except Poison) being rather useless outside Perseverance itself.