"Range attack affects adjacent hexes. Liches are the only range strike unit available to the Necromancer."
Liches are an undead unit associated with the Necropolises of Enroth, serving as a fifth tier unit in the video game Heroes of Might and Magic II: The Succession Wars and its expansion pack, Heroes of Might and Magic II: The Price of Loyalty. They can be recruited in Necropolis towns once the Mausoleum has been built, and can be upgraded later into Power Liches.
The only ranged unit available to the Necromancers in this game, their high tier makes them quite powerful, which when combined with their attack affecting all adjacent hexes to the original target makes them very dangerous, both towards foe and friend alike. Liches are best used against large groupings of enemies with as less allies scattered amongst them as possible to deal the most damage to a foe and as less damage to ones' own army as possible.
"Range attack affects adjacent hexes. The Power Lich has better durability in combat."
When their mausoleum structure is upgraded, subsequent liches to buy will instead be replaced with power liches, while existing liches can be upgraded for a price in that specific town, whether they were recruited from that town or not.
The upgrade increases their durability & hit points (allowing them to survive for longer), their speed (allowing them to move further when required to move), and also the number of available shots before the power lich is unable to use its ranged attack for the rest of the battle. Just like liches, power liches' ranged attacks hit all adjacent hexes and must therefore be used with utmost caution.