The corner blocks aren't needed for the performing Nether Portal, nonetheless, the portal that spawns in the opposite dimension when a portal is developed will consist of the corner blocks. An historic mob that is certainly hatched from sniffer eggs, which can be present in chests in underwater ruins. https://nether-portal-room13467.blogoxo.com/20070633/the-2-minute-rule-for-nether-portal-design