It just came to my mind that DI is possibly one of the most game changing spells.
How to make great use of it? Just cast it on the opposing mage and wait for him to cast a creature that costs alot of mana. During his "Cast Spell" step he chooses a target zone (since range is 0, its the zone he is standing in), he pays the mana (lets say 21 mana for legendary angel) and the spell has been cast. Now comes the counter spell step: You reveal DI and teleport him wherever you wish (not into the same zone). Next Step: Resolve Spell. Since the target zone, which has been chosen by the opposing mage during the cast spell step, is no longer valid, the spell is countered and all his 21 mana disappears into nothingness.
If you dont believe me check page 17 of the rules book:
When a spell resolves, if you find that the target of the spell
is no longer valid (has moved or changed), then the spell is
countered.
The downside is, that you need to save 10 mana (9 with ring of asyra) to be able to reveal DI. But what you get is incredibly powerful! Your oppent may lose much more mana than you paid, his creature spell is moved to his discard pile without any benefits for him, his mage is teleported to any zone you wish (and might need 2 rounds to come back to the spot he used to be, which gives you time to fight his creatures), and as a nice addition the priestess gets one extra life since DI is a holy enchantment.
Another neat trick:
As we all know, mage wands and elemental wands are very likely to being dissolved. DI is just another way to protect them for several rounds. If your opponent casts dissolve on your mage, reveal DI during the counter spell step and teleport him wherever you wish. He looses 5 mana, his dissolve spell goes to his discard pile (if your lucky it was his last one), and he needs one or two rounds to come back to you (which gives you plenty of time to make use of your wand).
In a similar way you can use it to counter devastating attack spells (e.g. chain lightning).
Even more deadly: If your opponent doesnt cast his spawnpoint early, try to lay DI on him as soon as possible. Use it to counter his spawnpoint cast, which gives you a HUGE advantage!
Until today I wasnt sure how useful DI is, in fact, i thought of removing it from my spellbook. But after thinking about it, DI might be the best spell of all that are available atm, at least its the most surprising one.
Actually, the ability to counter creature spells that might cost twice the mana of DI (adramelech costs 24 mana) seems so incredibly powerful - its hard to believe that this is how the designers intented it to work. But from my understanding of the rules, its possible ...