I had Keymaster Alabaster on the field and got a 1-cost copy of Golganneth the Thunderer. I wasn’t allowed to cast it even with ample mana.
Image: h ttps://gyazo.com/ec3fd78daba7d1fa5dc7dfb7c1f6cab2
There have been many bug reports lately about excavated / discovered / copied / generated cards being unplayable.