NHF – new heroes for Heroes V 3.1.

Wow, could you elaborate? How does it work (I have a vague idea), and how is it implemented (I have no idea)?

This is a standard spell.

Summon Hive - also known as Hive Transfer.

Materializes a wasp hive at the selected location on the battlefield. At the beginning of its turn, the wasp hive attacks the nearest enemy unit. This will continue until the end of the battle or until the hive is destroyed. The hive will not attack undead, elementals, or mechanical creatures. The hive casts the Wasp Swarm spell at the Expert level. When Wasp Swarm is cast, the mana of the hero who summoned the hive is consumed. Defense = 1*[Hero Level]. Immune to magic.
Effect at different levels:
[None]: Health=10, Initiative=2+0.25*SP
[Basic]: Health=25, Initiative=5+0.25*SP
[Advanced]: Health=50, Initiative=5+0.25*SP
[Expert]: Health=100, Initiative=10+0.25*SP

Source: http://heroes.ag.ru/heroes5/magic/schools/summoning/