SamplerEulerAncestral_SUN

Before you get too invested: this node no longer exists in the current pack. SamplerEulerAncestral_SUN shipped in the early versions of bvhari/ComfyUI_SUNoise and was deleted in the "Complete rework, breaking changes" update of July 2024, when the author folded all the per-sampler nodes into the selector nodes SamplersSUNoise and SamplersSUNoiseAdvanced. If you install the pack today you get v2.0.0, which doesn't contain it. I'll explain what it did anyway, because you clearly found an old workflow or an old page, and the knowledge transfers.

What it was

Euler ancestral is the workhorse of the ancestral family - the "creative but never settles" sampler that's been the anime-finetune convention for years. This node was exactly that sampler, with one change: instead of injecting standard Gaussian noise at each step, it injected scaled uniform noise, drawn from [-sigma_down, +sigma_down] and seeded deterministically from your sampling seed. The idea, straight from the SUNoise research that inspired the pack, is that Gaussian noise's extreme tail values cause oversaturation and "burning" at higher CFG, and a bounded uniform distribution sidesteps them.

Two inputs, both floats: eta (default 1.0), which sizes the ancestral jump, and s_noise (default 1.0), which scales the injected noise. Crank s_noise for more variety, drop it for more determinism. Output was a SAMPLER for the SamplerCustomAdvanced workflow - same wiring every sampler node in this pack uses.

Why you'd see it today

A workflow saved in the pack's first months (April–July 2024) references this class name by class_type. ComfyUI will tell you the node is missing. You have two clean options:

1. Upgrade the workflow: replace the node with SamplersSUNoise, pick euler_ancestral in the dropdown, choose noise_type. Same sampler, same noise idea, current code. One extra dropdown, no loss of functionality.
2. Pin the old pack if you must reproduce the exact old behavior: git checkout a commit from before the rework (e.g. efc6e38) in the custom_nodes folder. Old behavior is old behavior - you lose the interleaved-noise improvement of v2.0.0.

Installing (for the record)

The pack is on the Comfy Registry, so ComfyUI Manager → search "SUNoise", or:

cd ComfyUI/custom_nodes
git clone https://github.com/bvhari/ComfyUI_SUNoise

No dependencies, no model downloads, GPL-3.0. It's a tiny pack with no real community footprint, so there are no "known issues" threads to point you at - the versioning trap above is the main gotcha.

The bottom line

If your old workflow still runs on Euler a and you liked it, the modern equivalent is one dropdown selection away in SamplersSUNoise. And remember the pack's standing advice: these samplers want 30 steps or more, because low step counts don't give the alternating noise time to settle.