Blizzard has posted massive nerfs for Mythic Halondrus, Anduin and Jailer in Sepulcher of the First Ones on the Weekly Reset which includes 30 second bomb timers on Halondrus (up from 10).
BlizzardSepulcher of the First OnesHalondrus the Reclaimer
Time required for Volatile Charges to trigger a Charge Detonation increased to 30 seconds (was 10 seconds) in Mythic difficulty. Charge Exposure duration increased to 32 seconds (was 16 seconds) in Mythic difficulty. Earthbreaker Missile damage reduced by 20% in Mythic difficulty. Changed the pattern of Planetcracker Beam during Stage Three in Mythic difficulty. Reduced Halondrus’ health by 10% in Mythic difficulty. Reduced damage of Eternity Engine by 10% in Mythic difficulty.Anduin Wrynn
Anduin’s Despair and Anduin’s Doubt health reduced by 15% in Heroic and Mythic difficulties. Befouled Barrier’s absorbs 10% less healing in Heroic and Mythic difficulties. Fiendish Soul’s Soul Explosion missile travel speed reduced by 20% in Heroic and Mythic difficulties. Monstrous Soul health reduced by 6% in Mythic difficulty. Lost Soul’s Banish Soul cast time increased to 12 seconds (was 8 seconds). Grim Reflection’s Grim Fate haste bonus reduced to 200% (was 250%).The Jailer
Jailer’s melee attack decreased 10% in Mythic difficulty. Jailer’s health decreased 5% in Mythic difficulty. Martyrdom damage decreased 15% in Mythic difficulty. Torment damage decreased 10% in Mythic difficulty. Boon of Azeroth buff increased by 20% in Mythic difficulty. Read more on wowhead.com