Mark of the Shield: Buff can be any regular debuff spell (Cripple, etc). Upon cast, give the caster +MS ability and +armor ability. Use a damage detection system to check when the target is attacked, and if it's an attack not a spell. Upon attack, remove the buff and cast Inner Fire or something on the casting unit (to provide +dmg). Also create a dummy to storm bolt target. Also index the target so that when mark is concealed, he's added to an invulnerable group. Then check for closest unit and apply mark.
Furious Slash: On cast, enumerate all enemy units within hit radius. Check if any of them has the mark buff. If so, set some boolean "stunAll" to true. Then, create animation and of slash and damage each unit. If 'stunAll' is true, also create dummy and stun each unit based on Mark of the Shield's level. Also apply knockback. Also index caster unit to some hashtable or unit-indexing struct and increment his 'stacks' by 1. Create dummy and cast Cripple (or some attack speed modifier spell) on caster. This spell should have 3 levels (5/10/15 percent +AS) and be leveled based on stacks. Also remove Mark of the Shield mark from all targets.
Defensive Formation: Confuses me.
Holy Army: More or less Mark of the Shield detection. Rest is easy.