Wyverns

No, Paoka definitely doesn't deal damage to its own units. I've tried to make it happen, but it's impossible; I don't know where this information came from. As for which of these two upgrades is better, I think it's not that simple. People usually consider only poisoning a single stack, but you can attack one stack first, then another... How much damage will that be in total? Five units per turn for one Wyvern – let's say a Wyvern has 30 attack, which is 150 damage per turn, multiplied by three – that's 450. For example, 15 Bears (dwarven, of course), 30 Cerberuses, etc., will die, and no one will stop you from slowly poisoning the rest or refreshing the poison on the first stack. Of course, I doubt I've convinced anyone here, but in my opinion, you need to look not only at the obvious advantages but also at the hidden ones. And regeneration is definitely not a serious thing; it's just "a bonus."