Ok, ladies and gentlemen, lets see if we can't straighten this out, once and for all....
Horus LV8 said:
This card cannot be Normal Summoned or Set. This card cannot be Special Summoned except by the effect of "Horus the Black Flame Dragon LV6". While this card remains face-up on your side of the field, you can negate the activation and effect of any Spell Cards and destroy them.
Dark Lucius LV8 said:
If this card was Special Summoned by the effect of "Dark Lucius LV6", your opponent's monsters that this card destroys by battle are removed from play, and their effects are negated.
Level Up! said:
Send 1 face-up monster on your side of the field that has "LV" in its card name to the Graveyard to activate this card. Special Summon the monster that is written in the card text of that monster from your hand or Deck, ignoring the Summoning conditions.
Ok, now that we ALL have the correct text in front of us, lets dissect them, shall we...
1. "Level Up!" can be used to bring out "Horus LV8". That part is not in contention (I hope).
2. Why can it bring out "Horus LV8" when "Horus LV8" is a nomi monster? Because "Level Up!" ignores any summoning conditions, such as nomi-ism. Again, this part we all agree upon, yes?
3. Can "Dark Lucius LV8" be Normal Summoned? Yes. Why? Because it DOES NOT have any kind of Summoning Condition or restriction placed upon it. Will it have it's negation effect? No. Why? Because it was not Special Summoned via the effect of "Dark Lucius LV6".
4. Can "Dark Lucius LV8" be Special Summoned by "Call of the Haunted", "Premature Burial", or "A Hero Emerges"? Yes. Why? Because it DOES NOT have any kind of Summoning condition or restriction placed upon it. Will it have it's negation effect? No. Why? Because it was not Special Summoned via the effect of "Dark Lucius LV6".
5. What does "Level Up!" do? It Special Summons an LV monster. Can it be used to bring out "Dark Lucius LV8"? Yes. Why? Because it DOES NOT have any kind of Summoning condition or restriction placed upon it. Will it have it's negation effect? No. Why? Because it was not Special Summoned via the effect of "Dark Lucius LV6".
"Dark Lucius LV6" and "Dark Lucius LV8" have no Summoning Conditions at all...period. They have EFFECT conditions on them. "Level Up!" does not ignore these EFFECT conditions.
Make sense?
Good.
Hope this helps!