Undead Army is a two-orbShadowSpell that summons additional temporary creatures to the caster's side. This spell uses corpses in the spell effect to create Skeleton Warriors with their Unholy Armor enabled. This is also an interesting way to temporarily extend the duration of Skeleton Warriors that die after their unholy armor expires.
Gathers corpses in a 25m radius in order to summon a maximum of 4 Skeleton Warriors with their Unholy Armor enabled. For summoning a unit Skeleton Warriors 600 life points have to be gathered from corpses first. Skeleton Warriors have the same upgrade level as the spell itself. Reusable every 20 seconds.
Furnace of Flesh (FoF). Its ability is useful in any deck, if it can get the corpses. Soul Splicer is better at the gathering itself, with extended range,and can pass corpse energy to FoF etc.
Crowd Control Cards - Skeletons, being Small sized melee units, are vulnerable to all CC methods other than Mark of the Keeper, and the duration of the CC subtracts from their already short life expectancy.
Sacrifice Cards get a second advantage from units, whose corpses can then be gathered for Undead Army.
Embalmer's Shrine Decreases the number of corpses required to create the maximum number of skeletons.
Soul Splicer is the most adaptable way to gather corpse life points outside of the intended summoning area.
Nasty Surprise Makes maximum use of the doomed skeletons by turning them into damage before they die.
Soulshatter As Nasty Surprise; the skeletons that die during Soulshatter's duration will explode, but the skeletons also lure/keep enemy units in the killzone and do additional damage to aid Soulshatter in finishing off units.
Corpse Explosion An alternative, or as a finishing touch. Shadow Phoenix offers the ability to, effectively, get infinite Corpse Explosions for only the initial casting cost (bearing in mind the awkwardness of that unit's AI)
Motivate It is an easy mistake to make, to believe that a unit summoned by a spell is interchangeable with a unit summoned with a unit card. This is never the case. Undead Army Skeletons sacrificed with Motivate will aid other Undead Army Skeletons, but never regular Skeleton Warriors.