That's one heck of a commit you've got there...

I may have got a bit behind with version control. A lot behind, in fact. Maybe I'll go back and split this sometime - then again, I probably won't. But hey, at least it's here!

src/main/java/electroblob/wizardry/spell/Reversal.java

@@ -0,0 +1,83 @@
+package electroblob.wizardry.spell;
+
+import electroblob.wizardry.constants.Constants;
+import electroblob.wizardry.util.ParticleBuilder;
+import electroblob.wizardry.util.ParticleBuilder.Type;
+import electroblob.wizardry.util.SpellModifiers;
+import net.minecraft.entity.Entity;
+import net.minecraft.entity.EntityLivingBase;
+import net.minecraft.item.EnumAction;
+import net.minecraft.potion.PotionEffect;
+import net.minecraft.util.EnumFacing;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.util.math.Vec3d;
+import net.minecraft.world.World;
+
+import javax.annotation.Nullable;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class Reversal extends SpellRay {
+
+	public static final String REVERSED_EFFECTS = "reversed_effects";
+
+	public Reversal(){
+		super("reversal", false, EnumAction.NONE);
+		addProperties(REVERSED_EFFECTS);
+	}
+
+	@Override
+	public boolean canBeCastByDispensers(){
+		return false;
+	}
+
+	@Override
+	protected boolean onEntityHit(World world, Entity target, Vec3d hit, @Nullable EntityLivingBase caster, Vec3d origin, int ticksInUse, SpellModifiers modifiers){
+
+		// Naturally, this spell won't work unless it has a living caster and target
+		if(caster != null && target instanceof EntityLivingBase){
+
+			List<PotionEffect> negativePotions = new ArrayList<>(caster.getActivePotionEffects());
+			negativePotions.removeIf(p -> !p.getPotion().isBadEffect());
+
+			if(!world.isRemote){
+
+				if(negativePotions.isEmpty()) return false; // Needs potion effects to reverse!
+
+				// 1 effect for non-necromancy wands, 2 for apprentice necromancy wands, 3 for advanced and 4 for master
+				int bonusEffects = (int)((modifiers.get(SpellModifiers.POTENCY) - 1) / Constants.POTENCY_INCREASE_PER_TIER + 0.5f) - 1;
+				int n = getProperty(REVERSED_EFFECTS).intValue() + bonusEffects;
+
+				// Chooses n random negative potion effects, where n is the potency level
+				Collections.shuffle(negativePotions);
+				negativePotions = negativePotions.subList(0, negativePotions.size() < n ? negativePotions.size() : n);
+
+				// Now reverse them!
+				negativePotions.forEach(p -> caster.removePotionEffect(p.getPotion()));
+				negativePotions.forEach(((EntityLivingBase)target)::addPotionEffect);
+
+			}else{
+				ParticleBuilder.create(Type.BUFF).entity(caster).clr(1, 1, 0.3f).spawn(world);
+			}
+		}
+
+		return true;
+	}
+
+	@Override
+	protected boolean onBlockHit(World world, BlockPos pos, EnumFacing side, Vec3d hit, @Nullable EntityLivingBase caster, Vec3d origin, int ticksInUse, SpellModifiers modifiers){
+		return false;
+	}
+
+	@Override
+	protected boolean onMiss(World world, @Nullable EntityLivingBase caster, Vec3d origin, Vec3d direction, int ticksInUse, SpellModifiers modifiers){
+		return true;
+	}
+
+	@Override
+	protected void spawnParticle(World world, double x, double y, double z, double vx, double vy, double vz){
+		ParticleBuilder.create(Type.DARK_MAGIC).pos(x, y, z).clr(0.1f, 0, 0).spawn(world);
+		ParticleBuilder.create(Type.SPARKLE).pos(x, y, z).time(12 + world.rand.nextInt(8)).clr(0.1f, 0, 0.05f).spawn(world);
+	}
+}