The bottom line is, unless there are items or other on-board threats that require ink usage each turn, your opponent may not have a great use out of the ink to begin with
The good news is that it comes with 8 booster packs and is the same MSRP as 8 booster packs, so from that perspective its not bad value
If The Darkness Crystal leaves the battlefield at the same time as one or more nontoken creatures an opponent controls would die, those creature cards will be exiled and you'll gain 2 life for each of them
The four cost Snow White, Fairest of the Land is also worth to be considered as she can quest for two and cannot be changed
You don't need to wait for a five-cost Dragon Fire - anything from a two ink card like Freeze to ostensibly helpful actions like Healing Glow will do the trick
Most notably, if a triggered ability asks its controller to pay a cost, you pay that cost for the copy if you wish to have it paid