Trying to make Pure Harpies as consistent and competitve as possible, and I think I did a pretty decent job. I know there are 44 cards, its unfortunate. Small World helps a lot with getting channeler as often as possible. Trap Trick is to help get access to Harpie's Feather Storm as often as possible, as it is the card that wins you most of your games because of its insane negate effect.
After Some playtesting I found that 2 copies of Trap Trick was enough. I had one game where I banished one copy of Feather Storm off of Trap Trick and used the other 2 and it felt kind of bad to run out of them. Not sure that will come up very often where you will need all 3, since the game is so fast right now, but it did come up once which is why I'm only using 2 Trap Trick. Infinite Impermanence and Evenly matched are also great to run with Trap Trick just so that you have more than one reliable normal trap target.
All of the hand traps and kaiju, aside from Nibiru, that I chose work with Small world since they all only share 1 Type/Attr/Lvl/ATK/DEF with any of the Harpies. So, you can banish the hand trap from your deck to get to channeler. Nibiru is great with Cyber Slash, because you can just bounce the token on the following turn.
For the extra deck, I don't actually have S:P but if I did I would run it. If you don't have S:P, I would maybe run either Knightmare Unicorn (which is what I am running) or Wynn.
I removed Unexpected Dai from the deck because it felt more often like a dead draw than I would have it in my opening hand. Phalanx Pike feels pretty essensial to OTK's so I put it in the main Deck and added a second copy. I replaced 2 of the original Harpie Lady with a Cyber Harpie Lady and a Harpie Lady 1 since I'm no longer playing Unexpected Dai. Running 1 original Harpie purely for nostalgia, you could easily run another Harpie 1 or Cyber Harpie but I chose not too.
I took out Harpie Dancer and moved it to the side deck. It's normal summon effect doesn't come up very often. The only time you really use it is if you are going second, your opponent has backrow cards set, and you have access to Hunting Ground. I put in a second Harpie Queen in its place, although you could do a second Harpist instead. It depends on what you would rather have access to more often. The RotA effect from Harpist EoT is nice and all when activating Channeler, but I find that its more of a luxury than you actually need it. Harpie Queen feels much better as a 2-of because Hunting Ground is important to have for destroying Hysteric Sign to search 3 cards.
Edit: Ended up puting in Forbidden Droplet. It works incredibly well in this deck as another way to send hysteric sign to the GY for the search EOT together with the negate that it provides.
I might end up cutting Trap Trick and Evenly Matched, and see how it plays. Gonna do some more playtesting.