Wow, well, I got sucked into about 2.5 hours of Binding of Isaac reading.
If you gorged on the first game and think you're burnt out, I
dare you not to get excited about this.
First off, local co-op only.
The other player spawns in (can use a controller if you're on the keyboard) taking one of your hearts. They spawn as a little baby familiar like the ones in the previous game, but with full control, they fly and their attacks are identical to Isaac. Isaac retains control of the SPACE item and when it's used. When it triggers, it triggers for the baby as well. Babies can't pick up items at all though, and when they're spawned both they and Isaac's attack power is reduced slightly to compensate for all the spam. The baby can give their life back to Isaac at any time, which I imagine makes for some cool drop-in/drop-out maneuvers. But they can also take more life from Isaac (unless Isaac has 1 heart left.) So it becomes a kind of greed/need based co-op experience like Contra, where once you invite someone in you're kind of at the mercy of whatever type of player they happen to be. But there's more. Everyone thought co-op would be two Isaacs but McMillen wasn't having it. There's only one Isaac (sort of.) So how to keep co-op players enjoying the core fun of BoI, the randomness? When they spawn they spawn as one of many random babies, each with their own little things going on. There are also special rare babies that have abilities of their own separate from Isaac. But some babies are "cursed" versions of their better counterparts, so there's no telling what you can get. Characters like Cain and Eve ect.. will each also be able to unlock a specifically-themed baby just for them, that they have a higher % chance of spawning. Co-op players who despawn voluntarily respawn as the same baby.
Getting Platinum God in Rebirth will not be contingent on Co-op in any way.
-The visual overhaul. Lots of randomized ground clutter like pages and insects crawling around and non-enemy fruit flies. Water eventually running down the walls, randomized bits of nearly off-screen things like ropes and pipes and beams in the ceiling. New decoration/loot containers like pots. New and better fire and coils of poo. Better and gorier death effects.
-Light effects. Oooommmggg. To me BoI's utter lack of lighting was somehow part of the art style. But Rebirth is really the game McMillen wanted to make, and the lighting reflects that. Rebirth is swiftly becoming less cute and more genuinely disturbing just by that one change. It's not used aggressively in what's been shown off, but for example, Curse of Darkness is literally a curse of darkness on you now. The gifs on the blog look amazing(ly terrifyingly more difficult.)
-The Shop. It was basically another slot machine in BoI, a desperation buy or an excess buy. In Rebirth, it's going to take on a more central role in playing the game and take on a meta-game quality as well. First, more items period are going to be in the Shop's available pool,. Specifically, more items that contribute to play styles and builds. Some of that intent was in BoI already as you'd often get support items like Batteries or Ladders. Now it will extend to things like Life For Kill and such. McMillen really wants people hitting the shop more often than they were before, so they can tweak and specialize their build. In terms of meta-game qualities, the Shop will get a Donation Machine. Pitch in money and it eventually will upgrade the shop over several tiers, allowing it to offer more items of a potentially higher rarity (like unlock-quality items) and I guess some possibly shop-exclusive items? It will persist through games, and get accompanying visual upgrades. While you might consider this against Isaac's ethos it's really not. Item Unlocks follow the same principle, and all it's doing it increasing the attractiveness of spending your money at the shop (versus the Casino) and allowing you to cast a wider net for items that work with what you currently have, or just desperately need.
-Rooms. The total number of room combinations per chapter in BoI + WotL was about 150. In each chapter of Rebirth there will be
over 500 potential combinations. Some of these rooms will actually be dead-ends, something BoI didn't do very well. Lots of rooms will have at least 1 very rare alternate layout. There will be 5 new "Special Rooms" like Sacrifice Rooms, Arcades, Devil Rooms, ect...But the biggest new feature is LARGER ROOMS! Our Darker Purpose already did this, but whateve's. Rooms can be way bigger now, and while they're be rarer by far than single screened rooms, it allows for more dramatic room layouts, more room to manuever, larger enemies and more of them. McMillen also has way finer control over room rarity than he used to, so he's going to be adding a more flavor/theme rooms to the rotation, to keep up the game's rep for being mysterious and giving people something to puzzle over, in addition to all the story-telling benefits.
-1 revealed new playable character out of 5. And it's a doozy. So "Eden" will be a randomly generated character every time you play her. Him. It. Their stats, lives and two equippable items will be randomized within playable parameters. Their hairstyle will also be semi-random. But you can't play Eden whenever you want. No, to play Eden, you have to kill Mom. A lot. Everytime you kill Mom you kill a Mom Kill Token, which you can spend to play as Eden. (I think, maybe, you can even switch to Eden in game? Not sure.) Anyways, it's a calculated risk at rolling a beast character, or just because you want to play ultra-random mode.
-Status Effects on Tears. They've been greatly expanded both mechanically and visually. Instead of being a % chance to inflict their status, now they're basically an occasionally tear (at the most basic level) that inflicts the status when it hits. Enemies will get a visual that tracks the effect. One of the new status effects shown off is Fear.
-Numbers. Original Binding of Issac + WotL items: 198. In Rebirth: 450. Plus new common pickup items like Black Hearts (the opposite of Faith Hearts, which trigger the Necronomicon effect on screen when they're lost), double key rings, new cards, consumable battery drops to recharge your SPACE item, new pills, ect...50 new non-boss enemies, and 15 new bosses. "Double trouble" boss fights taking place in larger rooms will become more common. Rare spawn enemies and bosses will have their own special and unique ways of killing you, versus the lightly randomized parameters of before.
-Profiles for multiple players.
-The minimap can now be toggled between visible, hidden or transparent. Also holding the same key for long enough will cause Isaac to drop all of his currently held items.
-Daily seeds. This request came from LPers mostly, but, BoI will now expose the seed it used to generate each game, so you can hand that seed to other people and compete on the same basic run. A daily challenge seed will also be generated, and all you need to do is copy/paste it in when starting a new game.
-A few demonstrations of new items and trinkets. Like a set of Worm Trinkets that each modifies how your tears shoot, Metroid-style. There's a new item that makes your tears become independent shots which you can control instead of shooting them out wherever you're pointing, and walk them around to hurt things because they're no longer consumed on hit. And oh yeah, that completely sinks with everything else, so you get shit like this:
Oh yeah, you know want you want to see that shit with Brimstone.
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A trailer pitched at the consoles.At the rate it's going and the way they're sounding in interviews, I'm guessing the game is going to be late, late 2014. Maybe they're shooting for that Halloween release window, but McMillen seems content for it to take as long as it takes. They keep just piling in more features and stuff.