- A reference guide and manual in Russian for Heroes 3.

Are there any spells that have a very short duration and are independent of magic power? (like a force field)

FizMiG, sheet 02 "Spells used in HMM III". It contains information about the duration of each spell.

Also:
How does the "Luck" spell work when:
1) there is no "Air" skill
2) basic "Air" skill
3) advanced
4) expert
I mean, this skill increases the chance of success in percentages, but what exactly are those percentages?

+1 (no skill and basic), +2 (advanced and expert).

And the success rate is as follows: 4.2%, 8.3%, 12.5%. This is also available in the reference: Sheet 14, "Objects on the map that allow you to gain morale, luck, mana, and MP".