Sounds like Harab Raptors.
Flying units essentially teleport in battle -- they may move from any square, to any square. They may also retreat by moving off-map just as quickly.
Most flyers cannot fly in stormy weather,
but there are exceptions...
Sunray's guide --
http://www.freewebs.com/dominions2/units_dom3.zip
includes statistics of all the national units; independent units are listed in the 'poptype' sheet of the Excel workbook; as far as I know, there is no similar info sheet for all (1712 in the unpatched, unmodded game) units and commanders.