how do you dealing with black dragons as a mage ?
 

those black dragons are a real pain to deal with as a mage. I have found (i am sure i am not the only one^^) a good way to deal them massive damage with a combo with the green dragons to put them in a trap. But against great stack it is not enough to get rid of these and after the trap its a real nightmare:), so if someone as a good strategy ... post it please.

Since they are not affected by magic they are tough. Fire resistant units are good vs. them, like Demons and of course your own Black Dragons.

The basic strategy is to attack them with some worthless unit to absorb their counter attack then pile on with everything else you have. For a mage the best way to create a worthless unit is the Phantom spell.

there are lots of ways to OHKO dragons in most cases
* Skeleton archers (or elves) + Dragon Arrows
* Faeries (with the ring)

I casted Mass Dragon Slayer on my troops and threw in Knights into my standard troop layout after hitting Haas' Labyrinth.

If you're lucky to get some decent anti-dragon items, you can also wear the Shield of Rahha(+6 Defense, -50% attack of enemy dragons) and that sword that gave +5 attack and +50% attack against dragons; the green-hued one, can't remember the name of it.

If you use a single-stack dryad army, armageddon will destroy blackies. I didn't run into any black dragon stacks large enough to survive 3 armageddons in impossible.

I managed it with the mass dragon slayer spell + elves and hunters. Faeries kinda suck against them, since they have magical damage. Also the ghost sword spell goes through their resistance, so that's an option as well. And of course, the Reaper's Black Hole is wonderful. Knights are another nice option, and their speed is not that big of an issue since the dragons will come to you. Couple that with the sword and the shield that give bonuses against them + dragon slayer spell, and you've got a killer stack. The nice part is that they're in infinite amounts at the castle by the time dragons pose a real problem.

Since dragons have such a high initiative, investing in Readiness after hitting Demonia may prove useful.
Also, buffing high-initiative stacks (like lake fairies+Anga's ring) will allow you to have the first strike. Not spells on the dragon itself, but something else like spawning extra fodder units and place them on the dragon path, like Demon Portal, Phoenix, Phantom, Trap etc.

In KB there is no such thing as 'universal army composition'.

Now I realized I never tried TRAP on black dragons... does it actually work?

Yes but you need Green Dragons to drag them over it. Otherwise, they just fly past the trap.

All Dragons walk if the moving distance is two hexes or less.