EKJ would just be (mostly) an upgrade over
Fiend Hunter which I still like as a card.
What I dislike about EKJ is that on curve, the ability is a bit hit or miss. On the play, you will likely not hit anything and on the draw, maybe. Later in the game, it's very good though. You also lose out on
Fiend Hunter +
Sun Titan + sacrifice outlet if you care about that. At your power level, it feels like the card you want is
Skyclave Apparition, but it's obviously not a human.
Tidebender plays well and gives you a lot of play, love it. Only reason I exclude it is that I run Storm cards and that is hard enough to pull off.
I recommend
Winternight Stories. I was hesitant to add it as my only Harmonize card, but it's a simple enough mechanic to grok. With new releases, my cube is more and more GY and discard centric. In this context, Stories is both an enabler and a payoff and I am actively looking to increase the density of cards playable from the GY. I also like that it pushes Blue decks to care about creatures both with Harmonize and the actual discard ability.
Pyromancer is a cool one, but not a high pick I think. Works well with rummaging/looting, but that deck already has Tersa +Fable +
Seasoned Pyromancer as threes. It could work in spells matters with cheap cantrips, but the zero power is annoying as those decks are often tempo oriented. Slower decks with
Brainsurge and other draw spells might like it, but those decks are usually creature light, making the Pyromancer one of few targets. Not sure it has a great home.
I've been tempted by the Harmonizer, but I don't love its spot on the curve or the lack of evasion. Tifa seems like the way to go if you want to combo in that space.
Citadel is one of my favorite cards ever and I definitely would include it if I had
Tinker,
Dark Ritual and
Goblin Welder. It's really cool because it cheats on mana and cards, but you can miss sometimes. You have
Sensei's Divining Top as a combo with it, up to you if that is cool or bullshit.
The Endstone is one I recently added, with no real experience though. Working with lands opens the door to Green ramp or lands wanting it, which isn't always the case with these big artifacts. The life gain can be anti-aggro tech, forcing them to go big to take you out. It's also the kind of cheat target that will get you a lot of value, but won't end the game right away, giving a chance for the opponent to get back into the game and you to enjoy drawing a ton of cards.