I'm still here. Running out of ideas though. I think Black Orbs should be the uber rare "Wholly **** I GOT one!?" item of DMC5. Black Orbs always come in full, no fragments, and they up both your health bar AND your DT gauge. Also, DMC5 should be the first game to let you get Purple Orbs without buying them. Here's the Black Orbs item description.
"An arcane stone created from raw demonic power. It surges with energy, and will power up your abilities greatly."
I also have another idea for a gameplay mechanic. When you get low on health in DMC2, you could go into Desperation Devil Trigger, correct? I think this needs to be explained in DMC5. After getting it, there's an entire mission where you're stuck in DDT, and you gain the ability to use it freely after that mission. This is where another new orb idea of mine comes into play. It's called the "Rainbow Orb" and they're dropped about as commonly as White Orbs. Rainbow Orbs fill a "Desperation Gauge" that, when filled completely, allow use of the DDT for as long as the gauge lasts. Buying "Rainbow Charms" from the Statue of Time will increase the capacity of this gauge, and therefore let you use DDT longer.
No Nightmare weapon ideas, but good ideas for gameplay, right?