Something I accidentally left out of my analysis is that the upgraded crystal ball is somewhat OP.
Even though no number of crystal balls working together could guarantee a silence every turn, just 3 would give a 7/8 chance of a silence every turn, which is not something we would want.
Several ideas:
1) Make the crystal ball last for a set number of turns (maybe 3)
2) Drastically increase the cost of its ability.
3) Make it such that only one may be active at a time (when you play a new one, the old one disappears)
4) Give them a cooldown.
5) This is similar to 3. Make the crystal ball a shield. Instead of requiring 1
for the ability,
it could have the effect "If you took physical damage this turn, 50% chance of silencing the opponent next turn, 50% chance of being immaterial next turn. Immaterial"
Personally, I like 5 the best. Not only does it make it such that only one may be in play at a time (per person), but it also incorporates aether's trademark "Immaterial."
My favorite part about option 5 is that is provides an additional subtle nerf, which is that it, and another shield cannot both be in play at the same time. I think this would sufficiently balance the card, and would be add a fun, new dynamic to shields, which haven't seen much variation since wings.