What is this?

[spinbaby]

It’s growing in my mulch.

[The Velveteen Ocelot]

1. It's called "dog vomit" slime mold.

https://en.wikipedia.org/wiki/Fuligo_septica

I had some in my garden a few years ago. It likes mulch:

[spinbaby]

2. Thanks

Dog vomit does describe its appearance.

[The Velveteen Ocelot]

5. According to Scandinavian folklore it's the vomit of a troll cat.

Evidently troll cats don't puke up hairballs.

[JudyM]

3. Saw some over the weekend, it's aptly named.

[Binkie The Clown]

4. You discovered the illusive egg-fu-young plant.

Take cuttings and open your own Chinese restaurant.

Or maybe it's an omelette bush. They can be hard to tell apart.

[Botany]

6. A cellular slime mold

The fungus lives the majority of its life as mycelium but
When the conditions are right it puts up a "fruiting body" and that is what you are seeing here. This fungus is very important for healthy soils and the break down of lignins "woody stuff" into simpler compounds.

If you see it in your garden this what you should do... nothing.