What I know about slime mold will fit in this entry, but my fascination with it will not. Slime looks and acts like fungus sometimes, but then it up and moves. Time-lapse photography of slime mold on the move looks like a sentient creature on its way somewhere; this huge single cell can solve mazes (at least if there's a yummy sandwich at the end). Or sometimes it's not so much the moving as the design it makes as it expands: delicate lacery, shiny honeycombs, shapes that you cannot believe are natural, much less produced by such a 'primitive' life form.
Then they fruit. Sometimes the spore-bearing bodies look like mushrooms. The one I just found growing on a maple stump looks like it has little metallic balls standing on impossibly skinny hairs. How does this stalk, thinner than some spiderwebs, hold the ball up? Advanced materials science research, or just more primitiveness.
A single cell that can outsize any of us. That can move to get at something it has no organs to sense. That exhibits sublime engineering. That will outlast us all. Another evolutionary miracle.