Death Armour - Level 2 Necromancy

Discovered a stack of my old 1st, 2nd and 3rd edition books at my parent's home today, and immediately began ripping into them looking for stuff to nick for my 5e game. Of course, there is a stupid amount of great stuff, this spell (taken from the 2nd Edition Cult of the Dragon source book) being one of them; 

Death Armour
Level 2 Necromancy

Casting Time: 1 Action
Range: Personal
Components: V, S, M (Special ungent which costs 10 gps to make, and takes 2 full rounds to apply. This spell can be then cast within 8 hours of it being applied)
Duration: 1 minute per caster level (Concentration)

You shroud yourself in a crackling mantle of greenish black necrotic energy, which inflicts 4d4 necrotic damage to any creature striking you with a melee attack – although they may make a Constitution saving throw to negate this. This damage can affect a creature multiple times in a round, each time requiring a separate saving throw. Whilst this spell is active, you gain a +2 bonus to your AC.
If you are killed whilst this spell is active, you are considered to have automatically failed 1d3 death saves (which means you can possibly be killed outright).
At Higher Levels: When you use a spell slot higher than 2nd, this spell inflicts +2d4 more necrotic damage for every slot level above 2nd .

This spell is found on the Wizard, Sorcerer and Warlock spell list. It is also a 2nd level spell on the Priest's Undead Domain.