Reverse Batch Ovum

Reverse Batch Ovum takes a batch and hands you a new batch with the order flipped. Frame 0 becomes the last frame, the last frame becomes frame 0. That's the entire job, and for video work or any order-sensitive pipeline it's one of those tiny nodes you didn't know you needed.

It's the maintained batch variant of the pack's reverse family - the older ReverseList in the ovum/lists/any category is deprecated in the source, so this is the one to reach for when you want to flip a graph-level batch.

When you'd reach for it

ComfyUI's batch nodes frequently assume order, and sometimes the order you've got is the order you don't want. Reversing a batch of frames for a backwards playback effect, flipping a conditioning sequence, undoing an upstream node's reordering - all the same move: reverse it. Because it's non-mutating, the input batch is untouched, so it's safe to drop into the middle of a pipeline without side effects.

How it works

The backend is list(reversed(py_list)) - a new reversed list, not an in-place sort. The class declares both INPUT_IS_LIST and OUTPUT_IS_LIST, which is the signature of the ovum/lists/comfy family: the engine passes an incoming batch as a list and advertises the output as a batch that list-aware nodes can fan out over.

One honest caveat in the source: if you feed it something that isn't a Python list, it raises ValueError rather than guessing. That's arguably good behavior - a silent wrong answer would be worse - but it means you want to feed it real list-shaped data.

Inputs and outputs

• py_list (required, *) - the batch to reverse.
• * (output, declared list) - the reversed batch.

Installing it

Part of the comfy-ovum pack:

cd ComfyUI/custom_nodes
git clone https://github.com/sfinktah/comfy-ovum

Restart ComfyUI, or install via ComfyUI Manager → search "comfy-ovum". Lightweight dependencies, no models.

Common gotchas

• Batch dialect vs. Python-list dialect. This node talks graph-batch. If you're feeding a Python-list utility that wants a single list object, use ReverseListOvum instead.
• It reverses, it doesn't sort. No keys, no comparators, no options. Wrong tool if you actually wanted ordering logic.
• Non-list input raises. Get a confusing error? Check that py_list is genuinely list-shaped before wiring it in.