Epic effects were compilations of sound effects (most of them are sound files from the Half-Life games) mashed into one, larger and more awesome sound effect. This very thing was only used by Coulden, and was used on various grounded videos that have to do with Resonance Cascades, bombing runs, Strengths and Powers of Street Knowledges, etc. Epic effects are frequently used in full-length movies like Coulden's Erika Adventures: Makron's Revenge.
Many sound effects are explosion-type sound effects (oftentimes loud), and always consist of explosions coming from grenades, RPGs and Satchel Charges, and electrical zaps coming from Vorts, Alien Controllers and Nihilanth throwing energy balls. Larger Half-Life 2 explosions are sometimes used. The origins of these epic sound effects were from a program called "GCFScape", a program that lets you open up .gcf files, and "Steam", a digital distribution, digital rights management, multiplayer and communications platform developed by Valve.
An epic sound effect was made by using Sony Vegas Pro 11, one of the software that Blue Mario actually uses to create some videos.