Simple Summary: Endoparasites such as Ascaris suum can pose a serious threat to the health of livestock and, consequently, humans. One promising way of controlling the threat is the use of natural enemies/antagonistic fungi. In this study, we examined the effects of entomopathogenic fungi (naturally attacking insects) as a bioregulator in the invasive stages of the parasitic nematode A. suum. The conducted study indicates that none of the fungal strains tested have nematocidal activity against A. suum eggs, and they do not meet the criteria required for use in the bioregulation of the parasite's dispersal stages. Among the strains tested, Isaria fumosorosea and Metarhizium robertsii stood out, combining the highest metabolic activity with nematocidal activity against A. suum. The aim of the study was to evaluate the potential of using five selected species of entomopathogenic fungi (Beauveria bassiana, B. brongniartii, Conidiobolus coronatus, Isaria fumosorosea, and Metarhizium robertsii) in the bioregulation of the dispersive stages of the parasitic nematode—Ascaris suum. Experimental cultures of each of the selected entomopathogenic fungi, as well as a control culture without fungi, were incubated with A. suum eggs at 26 °C for 28 days. Development of the A. suum eggs was observed using a light microscope on the 7th, 14th, 21st, and 28th days of incubation. The API-ZYM® test was used to determine, semiquantitatively, the activity of 19 hydrolytic enzymes from the entomopathogenic fungi. The cytotoxicity of the fungi was determined using tetrazole salt MTT. It was found that none of the five tested strains of entomopathogenic fungi showed an ovicidal effect, and none of them colonized the A. suum egg shells. However, ovistatic activity was observed mainly until the 14th day of incubation by I. fumosorosea, M. robertsii, and B. bassiana. In the MTT test, M. robertsii showed moderate cytotoxicity, while the other species showed low cytotoxicity. Among the strains tested, I. fumosorosea showed the highest spectrum of hydrolase production (13 out of 19 enzymes gave a positive reaction from 3 to 5; 20–40 nM or more). The absence of morphological changes in the A. suum egg shells suggests that the antagonistic effect of the studied entomopathogenic fungi may be due to their cytotoxicity, associated with the production of secondary metabolites—toxins (M. robertsii) and enzymatic activity (I. fumosorosea). [ABSTRACT FROM AUTHOR]