Protego Diabolica (Dark)
A dark-tier add-on spell for SpellCraft - Magic World (Arcanum). It does not edit the base mod's jar — just drop it in and a new spell shows up in your grimoire.
Coexists with Arcanum's own Protego Diabolica. The base mod's version is an Advanced protective aura that shields you, knocks attackers back and sets nearby foes alight. This is a separate, darker take — a faithful, lethal Protego Diabolica that doesn't push enemies away… it ends them. Both spells live side by side; this one appears in the menu as Protego Diabolica (Dark).

What it does
Cast it and a stationary ring of soul-fire ignites around where you stand. It holds its ground — it does not follow you.
Instant death on contact. Any creature hostile to you that crosses the ring is slain on the spot — including flyers, up to ~6 blocks high. Peaceful mobs walk through unharmed.
A wall against spells. Enemy spell rays clip against the fire like a true barrier — think Priori Incantatem. A spell cast into your ring from the outside fizzles at the flames instead of hitting you. Death Eater casts are cancelled at the wall.
Snuffs out projectiles. Arrows and thrown projectiles from enemies die at the edge.
PvP-aware. By default any other player entering the ring is slain. Teammates are spared automatically if FTB Teams is installed (optional), and you can keep a manual allow-list with in-game commands — no FTB Teams required.

Companion spell — Diabolica Lash
A whip of soul-fire that only works while you stand inside an active ring. Lash it along your aim and it instantly slays the first creature it strikes, carrying the ring's death out to a target beyond the flames. Uses Arcanum's native beam, tinted soul-fire blue, fired from the wand tip.

Config

config/protego_diabolica.json lets you tune:
Duration of the ring (seconds)
Mana cost and XP cost (in levels) to cast
Lash mana cost, cooldown and range

Cooldown is intentionally left to Arcanum Tweaks (my companion add-on) if you want to reshape it per skill node.

Commands
/diabolica allow <player> — spare a specific player inside your rings
/diabolica remove <player> — remove them from the allow-list
/diabolica list — show the current allow-list

SpellCraft - Magic World Protego DIabolica addon

FTB Teams (NeoForge)

SpellCraft - Magic World