Gliscor (and to a lesser extent, MLatios) should be consider like Gastrodon I believe. Gliscor actually can switch in any non Z fire Heatran and kills it with earthquake. Z fire actually claim the kill after stealth rock, but firstly: we talk about a leftovers tran, which is easy to spot early in the game, and so, what about Z grass/nature power Heatran ? It's not as seen as Z fire, but still exist. Basically, they are all counters, but not SSI, even MLatios which is only threatened by Z Steel, not the most common set played on Heatran (actually a lure set, like Z grass), can be consider like that. Only Spdef Zygarde with rest can freely switch on any heatran and kills it without any risk.