Heroes 5.5 WarGame Edition - Tactical Edition.

It's unclear how a living creature can resurrect by eating someone. Also, it seems that the poisonous wyvern is somewhat weaker than the other two in terms of abilities.

It's very simple if you consider that the killed are just mortally wounded and incapacitated (taken out of action). Wyverns eat, wounds heal, and combat ability returns.

Also, it seems that the poisonous wyvern is somewhat weaker than the other two in terms of abilities.

Poisonous wyverns (winged creatures) have a very strong poison, but to maximize its effect, you need to try to bite units with high defense. However, in terms of resurrection abilities, they are indeed more convenient.

Added 3 minutes later
Regarding mod names, links to download them are needed.