Interesting niche card.  TCG Exclusive.

Pilgrim Reaper

This gains 200 ATK for each DARK monster in both player's graveyards.  One problem.  Most of the time, your opponent won't have a lot of DARK's in the grave.  And early on, you won't either.  10 DARK monsters puts this at a passable 2000.  15 for 3000 is even less economical.  20 DARK monsters is really situational.   If your opponent has a graveyard with DARK's in it, chances are they are going to benefit from this card's milling effect as much as you are.

People summon LV6 monsters to devastate their opponent; not to mill their deck by 5 cards.  If you can keep this card alive for another turn, that's 10 cards, but otherwise the opponent will be able to survive.  In an era with tons of revival options and graveyard advantage, this card may help your opponent.  And that's bad.  I'm sure even dedicated mill decks have better options.  If you want to mill cards, just use a Lumina + Raiden combo.  You can mill 7 cards that turn for yourself if you want.

Even though there aren't a ton of generic rank-6's, this card still faces stiff competition.  Photon Strike Bounzer is usually your best LV6 bet with 2700 ATK and monster effect negation.  Constellar Ptolemy M7 also has its share of viable combos on top of being a 2700 beater.  Gauntlet Launcher can take out two monsters with its ability. 

Perhaps in a deck that focuses on rank-6 monsters can splash a copy of this card in.  If you're looking for one or two generic rank-6's, though, there are much better options.

Assessments

Power – 2/5 ; Low ATK, and usually not threatening in any sense.

Versatility – 1/5 ; Very situational.  I could see it as a way to end the game if the opponent has a really thin deck, but that's it.  Weak ATK if your opponent has no darks.

Dependability – 1/5 ; Low marks.  Milling is totally random.  You could mill nothing good while the milling effect ends up helping the opponent.

Card Advantage – 1/5 ; You might be able to gain some advantage off the mill, but enough advantage to make up for 2 LV6 monsters?  Nope.

Speed – 3/5 ; Ignition effect.

Ratings

Traditional – 1.75/5

Advanced – 2/5

Verdict

Not an excellent card, but who knows what combos people might stumble unto. 

Pilgrim Reaper

Firstly, Pilgrim Reaper starts off with an indeterminable (or ?) attack as well as defence. For every Dark monster in either players Graveyards, this card gains 200 ATK and DEF, which while at first glance may seem quite reasonable, in all reality, it’s simply quite unspectacular as at least 10 Darks are going to be required to make any sort of real impact regarding this cards stats. And even in a dedicated Dark Deck, boosting it to an acceptable level or attack where you can actually start to run over some big stuff is not going to be very likely.

As for it’s effect by detaching 1 Xyz material from this card you’ll be able to activate it’s effect of sending 5 cards (or up to if less than 5 cards are remaining in Deck) from both players Decks to their respective Graveyards. Now while this may serve to be quite useful in potentially boosting this cards stats, as well as putting key pieces into your Graveyard, the issue with this cards effect is that it essentially helps your opponent out just as much as it does to you, and if you were to use this effect against an opponent playing Lightsworns, Chaos, Shaddolls, Bujins… Basically any Deck that wants monsters/ specific cards to be sent to the Graveyard, this card suddenly becomes your worst enemy.

That is unless you’ve Summoned it when your opponent has only a bare few cards remaining in their Deck, and you are going to be able to use it to essentially Deck them out… Then, good play to you sir!

Once released, Pilgrim Reaper combined with Rank-Up Magic Astral Force will allow the Summon of Number 23: Lancelot, Ghost Knight of the Underworld who will be equipped with 3 Xyz materials rather than the normal 2… So if you can protect it, it can quite easily be an extremely difficult card for your opponent to get around… Much like Light and Darkness Dragon is for some Decks.
Sadly though, this really isn’t an example of the benefits of Pilgrim Reaper as a card, this only shows that it could be used as a stepping stone for the Summon of Number 23.

Pilgrim Reaper also potentially provides a boost to Vampire/ Zombie Decks if Vampire Kingdom is on the field, however it really does require quite a bit of effort for what ultimately results in only a minimal overall boost for the Deck.

Although before completely writing this card off as basically useless, it did occur to me is that Necroface is currently at 2, and this got me into thinking that it may be useful as part of a Necromill Deck as Necroface and Soul-Absorbing Bone Tower form important aspects of that Deck.
Being used in this way may actually make it a more valuable card than when considered being used in any other way… Or at all!!!

Traditional: 1. No words can truly describe how badly it would be here… And neither does the score of 1!

Advanced: 1. The best real possible use of this as I see it will be when Number 23: Lancelot, Ghost Knight of the Underworld is released, otherwise it’s only going to be good if you can send from your opponents Deck to their Graveyard something that would otherwise be irreplacible… A piece(s) of Exodia perhaps???

My final note on Necromill however, may suggest an actual and surprising use for this card after all.

Pilgrim Reaper
 
From a new Fusion Monster to a new Xyz monster; Pilgrim Reaper. Statwise Pilgrim Reaper is a Generic Rank 6 Monster which is always good.  It’s a Dark Zombie, which is also good with ? ATK and DEF, which we will look at with the effects.
 
Speaking of Effects, its ATK and DEF are determined by the number of DARK monsters in both Graveyards, since 200 ATK and DEF isn’t a massive boost and it has no base stats, this is only really useful late game.
 
Pilgrim Reaper’s other effect is a good old fashioned mill effect, which forces both players to mill the top 5 cards of their deck, for the cost of 1 Xyz material. Obviously the idea here is to get more DARK monsters into the graveyard. While I love mill cards, they are these days a bad idea, as a lot of decks and cards benefit from having cards going to the graveyard, so while you might get more ATK and DEF, you probably will be helping your opponent out as well. Also it does force you to mill as well, but if you are using this card in either a zombie or DARK deck this probably will help you.
 
Overall, it gives Zombie decks another Xyz monster to play with, but its main effect could easily aid your opponent more, use at your own risk.
 
Traditional: 2/5
Advanced:  2/5

Pilgrim Reaper is on deck today. a Rank 6 Xyz monster, needing any two level 6 monsters to summon. A DARK/Zombie with ?/? for ATK/DEF, but it gains 200 ATK and DEF for each DARK monster in both players graveyard. Once per turn, you can detach 1 Xyz material from this monster to have each player send the top 5 cards from their decks to their graveyard. If you are using Pilgrim Reaper, it should come with a warning label: USE WITH CAUTION. Milling might seem like a good idea against some decks, but if you do this against the wrong deck (IE: Lightsworn) it will explode in your face real quick. Also, this card may not see over 2000 ATK/DEF in some games, depending on what deck your opponent may be using, so it might not even stay on the field that long. I will say, that this card is an Exodia's player worst nightmare. I can't see this card in too many decks, with Vampires coming to mind first. It has a good idea, but in this format, a lof of deck wants certain cards in the grave.
 
Traditional: 2
Advanced: 2

The best way to view the Extra Deck's as a 15 card toolbox, a way to solve your problems and push you towards victory. Generally speaking, no Extra Deck monster is terrible because they all fit into different niche spots. Even "bad" cards like Submersible Carrier Aero Shark technically have uses. Back in Dino Rabbit format, this card saw brief use as a Rank 3 out to Gellenduo in the mirror match. Sure, it only had a brief time in the spotlight but 15 seconds of fame is better than no fame at all, right?

Pilgrim Reaper fits into the "kinda has one neat use" category, but it just isn't that strong to get anything going for you. For every Dark monster in either player's graveyard, Pilgrim Reaper gets a 200 ATK and DEF boost. Early in the game, Reaper will have basically no attack points. Even if you're playing against a Dark World or Shaddoll deck, you'll be lucky to have Pilgrim Reaper with more than 2000 ATK.

For better or worse, it's a Rank 6 - an Xyz Rank that doesn't have the most support. Outside of Hieratic decks, there isn't really a good deck that spams Rank 6 monsters. The cards are a bit stacked against Pilgrim Reaper, but its effect makes it semi-useful.

One per turn, you can mill the top five cards from both you and your opponent! It's not very good to mill things like Burning Abyss or Shaddoll monsters, but hey, if you're looking to deck out your opponent, there's now an Xyz for that card. Obviously you'll be milling for yourself, and that's the important part. It's saving grace is that it's a Rank 6, meaning that even if it has piddly attack after you use its effect, you can stack a Gaia Dragon, the Thunder Charger on top Pilgrim Reaper so it's at least useful.

Traditional: 1/5
Advanced: 1.5/5