Visual bug with 1 mana blue permanents and Defiler of Dreams
I had a Defiler of Dreams in play and a Tolarian Terror in hand. There were more than 6 instants and sorceries in my graveyard, so Tolarian Terror's cost was reduced to one blue mana - made Phyrexian by Defiler of Dream's ability. Additionally, my mana was completely tapped out.
Tolarian Terror was not highlighted in my hand as playable cards always are - I was able to drag it to the playing field and cast it for two life using Defiler of Dream's ability, but the interface suggested that it was not cast-able.
My suggestion would be to highlight cards that cost just one Phyrexian mana even when you're tapped out of mana, as they are still castable... as long as you have two life.
Steps to reproduce:
1. Have Defiler of Dreams in play
2. Have 6+ instants/sorceries in the graveyard
3. Have Tolarian Terror in hand
4. Have no mana available, either in the pool or in untapped generators
5. Have 2 or more life
5. Observe that Tolarian Terror's cost is reduced to {U/P}
6. Observe that Tolarian Terror is not highlighted, making it seem unplayable
7. Play Tolarian Terror for two life, confirming that the interface didn't realize you could take the action you were allowed to.
Log from draft match attached. Screenshot and screen recording from re-creation in a bot match attached as well - it looks like anything that costs 1 is similarly affected.