Shadow King idea is awesome i might do something similar for my first boss if u dont mind. With all them abilities hed be finished in no time. :O As for some other abilities for the shadow king, im thinkin somethin like
Strength of Souls - Whenever the Shadow King kills a unit he gets a small HP, MP, attack power, and attack speed bonus. Whenever it turns day time he no longer gets bonuses from killing units and upon daybreak, he turns back to normal.
Maybe also make the boss have phases, and he only uses certain abilities depending which phase hes in. Also if hes a shadow king why not have him turn into a shade by day (invulnerable shade of course) another good ability might be
Dark Feedback/Shadow Feedback - This ability can only be used if he has cloned you or himself, the clone is instantly destroyed and he regains 80% of the cloned units current health.
As far as the phases go if you would like to use that idea then possilby something like
Phase 1: Organic - During this phase the Shadow King is just like any other unit, in fact, he IS any other unit, he is hideing in a pack of other units of the same type, you dont even know he is the shadow king until you attack him. When you attack him Phase 2 begins.
Phase 2: Shadow - Once you attack him he changes color to a darker version of himself. (To do this use the unit-replace unit trigger) He gains all the abilities you described except any of the cloneing ones, during this phase he has extreme hit point regeneration during the night and none during the day, when he reaches 40% HP Phase 3 will begin.
Phase 3: Shadow King - During this phase he will take damage over time during the day and extreme hit point regeneration during the night. Also he is now only vulnerable during the day (Whereas before he was only vulnerable during the night) and he gains all the clone abilities you described. When this phase begins he summons ten ghosts that line up in a circle around the edge of the room. Every 20 seconds he uses Strength of Souls on one random ghost to regen HP. Each ghost has 500 HP and will resurrect the boss in phase 1 if the boss dies. All ghosts should be destroyed before you kill the boss. Once all the ghosts are dead, the boss will enrage for +30% attack speed and also gains,
Call Spirits - Summons 3 ghosts who will spam AOE spells at the enemy, these ghosts cannot be killed or destroyed with Strength of Souls, Once he uses this spell once, he will then spam it every 30 seconds at a rate of 1 ghost/cast.
When he gets down to 10% health a green ghost will spawn at the entrance of the room. This ghost has VERY low movement speed and will heal the boss to 100% health if the ghost gets within collision range with the boss. If the boss is healed this way he will remain in phase 3 unless the player(s) is dead (dies)
I know i made this thread with help for some of my own bosses but i couldt resist making some suggestions. Again the shadow king is a great idea, lemme know if i could use it in my map. Thanks :}