really nice coral. can’t help with age

Agatized wood is a thing. It’s a beautiful piece.

Not a fossil, but a nice piece with quartz or calcite crystals. To tell which it is you can find an inconspicuous place to scratch or drop an acid (vinegar is ok, I find lemon juice sometimes works better). Calcite will scratch or fizz, quartz will not. Sometimes it’s easier to hear it fizzing than see it.

nice ammonite

Any more info like location or how you got it? Reminds me of Helicoprion but that’s very much a guess on my part.

For sure not an embryo. Looks like a very worn horn coral.

Not a horn coral. May be an internal cast of an oyster. Looks like possible shell imprint also (ridges on bottom center of first picture).

Look at bubblegum agate. I wouldn’t call this exemplary of it, but I think it’s a good match. If you are in Rapid City the university (? been a few years) museum has nice examples of agates and other minerals, and possibly people who can identify for you.

out of focus, but looks like classic agate with the banding.

Ignore the above comment. Assuming the first picture is your leaf guess. It’s a brachiopod of some sort. It looks to me like it was open all the way when it fossilized. There are always a few “creative” people on this app, right now there are a lot of them.

Just coming by to say the size of the rock has nothing to do with it containing fossils. It’s about what kind of rock and where from, not the size.

Manganese dendrites. not fossils, but commonly mistaken for them. These are some nice examples

Location helps to identify. City name at least helps narrow the age of the area for more accurate info.

Baculite

If it’s fossil you need to include location info so someone can look up the age of the rocks. Photos of other angles will help too, though it may be too broken to be very certain.

“toe” bone

you might find it as a septarian or septarian nodule in English

looks more like volcanic landscaping rock than a fossil. What is the white bit on the right /underside?

if it’s not real might be a replica, some formations have fish like this commonly. The green river formation in the US is famous for it.

Turtle for sure. The texture in the second picture is very turtle, and in the side shot you can see a bone texture.