Reminiscent of Lingering Flame from Dark Souls II, this spell creates a trap in the form of a timed mine. However, unlike the aforementioned spell, this pyromancy neither lingers in the air nor waits until a target approaches. Once launched and stuck to a surface (any surface except enemies), it will charge up and then detonate after roughly four seconds for great damage. However, if thrown directly at a target, it will deal about half the damage and the mine will be consumed and not detonate.
Though this pyromancy is a very situational spell, if the explosion hits, it deals even higher damage than Chaos Bed Vestiges.
Some measure of planning is required for this spell to be effective. In PvP, this is rarely a good spell to use unless it is stuck to an obscure location that the other player are likely to miss. It can be used as effective area denial, though. However, this spell can shine in PvE with some careful thinking. It can be free-aimed like your typical fireball spells, and as such can be stuck to ceilings and walls. For example, in The Ringed City, where there are enemies clinging to the wall, this spell can be thrown next to them without having the enemy triggered and it will inflict massive damage. It can also be set up in the path of an oncoming enemy if you know their path trajectory. Always keep the timing in mind as the spell will not automatically detonate once an enemy gets close (it should be noted that some enemies do seem drawn to it).
It is not advisable to use this spell while locked-on to an enemy as it will throw the spell straight at them which will cause it to hit like a fireball and cause much less damage. This pyromancy is best utilized with free aiming (which has always been a staple strategy of pyromancy). Seething Chaos may or may not hit through walls, it mostly depends on the thickness of the walls.