See title. There is just nothing you can do against this card. Other powerful cards, like Fire Witch, at least have counters. There are a number of ways you can prevent the special from going off. Hellfiend special has no counters. Even if he is spawned in the middle of a chilling wind and frozen before he appears (there will be only an empty space with a healthbar) he still does the 1200 special damage. You cannot prevent it. Combined with being spawnable everywhere on the field (for some reason he’s the onlly card that ignores spawn place rules), costing only 6 mana and having a high attack value, he’s stupidly powerful.
At this point I’m so sick of playing against this card that I honestly want to stop playing every time it appears. Just let the opponent win. There’s no point anyway.