Lothrik

Gorefiend's "berserk" is Soul Sunder. He casts it after the 3rd Feast of Souls ends, and thus it does not have a fixed time where it occurs. For most guilds this will happen around 9m-9m30s into the fight. No public logs exist currently where a guild has killed Mythic Gorefiend after Soul Sunder went out, but it's definitely possible to survive 10-15 seconds into Soul Sunder with Spirit Link bypassing the -100% Healing debuff.