Alien Like Growth

Its just something in your substrate. All kinds of junk is in potting soil. Even pure coco i've had liberty cap mushrooms grow in it. Spores are always present in the air. Its no big deal. Just pull that shit out of there. By the way, there's another point in the corner of bottom watering. Top layer of soil is always dry, that mean fugus gnats cant live and spores and little foreign seeds can't germinate.

Just kidding (Saxifraga paniculata, with a little help of https://identify.plantnet.org/k-world-flora/identify).

liverworts - definition As we just mentioned, the first thing to note about liverworts is that they belong to the class of bryophytes, being non-vascular plants, meaning they lack a vascular system responsible for the transport and conduction of nutrients and substances internally. They are also called Hepaticophytas, Marchantiophytas, or Hepaticae, although it is common to simply refer to them as liverworts. They receive this name due to the resemblance that some of these small plants have to the liver, which is why they were used in the Middle Ages to treat diseases of that organ. What you have there is Marchantia It belongs to the family Marchantiaceae, whose most notable characteristic is its intense green color. Some specimens of this species can reach up to 30 cm. They generally grow in mountainous regions and use a rock to anchor themselves, thus obtaining a greater reserve of moisture.