Recent observations of the isotropic diffuse gamma-ray background by Fermi allow us to get more insight into distant very-high-energy (VHE) and ultra-high-energy (UHE) gamma-ray emitters, including cosmic-ray sources. The Fermi data are well above expectations for an attenuated power law, which may suggest a possible VHE Excess. We consider its origin and show the importance of intergalactic cascades induced by gamma-rays and/or cosmic rays (CRs) for astrophysical scenarios. The relevance of the cascades is also motivated by possible VHE excesses found in some TeV blazars, which requires very hard intrinsic spectra. They are also important to constrain the UHECR origin and dark matter, as well as neutrino observations by IceCube. We may discuss possibilities of transient cascade gamma-ray sources.