Mortis Engine Warhammer fantasy battle 8th Edition overview for Vampire Counts
What is a Mortis Engine
In terms of game fluff the Mortis Engine is a bizarre and macabre reliquary build of unsavoury materials such as bones. These are constructed to contain the remains of a powerful past Vampire or Necromancer. Powerful spells bind evil malignant spirits to be the guardians of the Mortis Engine, in battle these bizarre contraptions of bone and metal borne aloft by evil spirits soak up the abundance of dark magic invigorating nearby undead and stealing the life force of nearby living creatures, the longer the battle rages on the more concentrated and deadly the Mortis Engine becomes.
In the Game
In the game the Mortis Engine is a bizarre chariot with potent abilities with a strength of 5 (of of course impact hits from being a chariot) and toughness and wounds of 5 along with regeneration making it quite survivable. The Reliquary special rule grants a special bonus/attack in a random determined area at the start of every turn this grants any nearby undead a bonus of +1 to there regeneration save (or gives them one of 6). It also causes a random number of hits to any enemy units in range these have a strength equal to the turn it is so the Mortis Engine becomes more dangerous with each turn that passes. Lastly if the Mortis Engine is destroyed it explodes in a large area take a substantial number of hits with a strength equal to the turn that it is.
Pros and Cons
The Mortis Engine is a Large Target and the model itself is quite tall and given that it explodes causing damage to nearby units it will become a magnet for missile fire and particularly war machines (particularly the dreaded flaming Dwarf cannons). This of course varies as to what army your opponent is playing with. With both impact hits, Banshee Howl attack and a substantial number of strength 3 attacks in can be effective in combat whilst causing further damage to the enemy and boosting your own troops. The +1 to regeneration particularly benefits Crypt Horrors, Terrorgheists, and Strigio Ghoul Kings.
The Mortis Engine is best used as a support unit enhancing nearby undead units and damaging enemy units. Generally it is only best to throw it into combat against small, low toughness and armour save units or combats where it will generally help you out. It is worth mentioning the Blasphemous Tome upgrade granting nearby wizards a bonus of +2 to casting spells from the Lore of Vampires (it is worth noting this also affects enemy wizards using the lore too!). This is a great boost to casting Invocation of Nehek and other low casting spells. This comes at the cost of worse miscasts so it is generally best to leave your more powerful casters and particularly your general out of range.
The Mortis Engine synergises well with units that already have the regeneration special rule and the damage it causes to the enemy, however a canny oppenet will know this and likely make it a priority to destroy the Mortis Engine.
Another interesting tactic potentially usuable in the later stages of the game (as the damage it deals will be at a much higher strength by then) is the suicide assault charging it into a powerful enemy that will destroy causing it to explode and hopefully take half the enemy army with it. This can also be useful to make sure a badly wounded Mortis Engine is out of the range of most of your army as a safety precaution. The Vanhel's Danse macabre spell can be useful to give the Mortis Engine that extra movement.