Abilities- Ranged curse that slows defensive structures attack speed, or just a damage over time curse that is an area of effect attack. Additionally it would have an occasinal healing aoe burst than can only heal dark troops within range for 8-10% of their health per burst. Bursts say every 15 seconds.
I think it would be a good addition and add more strategy to already existing characters. Ex: Level 1 hogriders are somewhat weak in hitpoints but with a dark priest you could extend their lifetime by a few seconds possibly.
Of course if you have more than one dark priest their curses and healing potential would not be able to stack multiple curses or healing would not stack. No double cursing an area, no double healing either. Set percentages for determimed area. However as long as the priests aoe dont intersect each other u could curse/heal in more than one place at a time.
Would it be realistic? If they made a troop like that, it seems like it would have to go in a level 5-6 dark barracks. By the time you upgrade to that level, your hogs are probably going to be upgraded beyond level 1 (hopefully at least), so could it help? I currently only have level 1 hogs and I hear from other people that they are only really good once you level them to 4 or 5, so I guess your troop could help up to that point. Just trying to offer a different aspect, but I'm not sure my thought would be completely accurate .