RowDog Like I said, phys defensive slowbro is one of the best darm counters in UU, so it's not surprising that if slowbro is at full health, darm cannot muscle past it by clicking on flare blitz (we would generally call the ability to muscle past any counter with a single move "broken"). Good news is that contrary to popular belief, darmantian has 3 other moveslots. Here's one that I want to draw particular attention to...
252+ Atk Choice Band Darmanitan U-turn vs. 252 HP / 252+ Def Slowbro: 180-212 (45.6 - 53.8%) -- 2% chance to 2HKO after Leftovers recovery
If you predict the slowbro swap in and u-turn out to something that can threaten him out (such as any volt switcher not named forretress), that slowbro has no choice but to swap out and hope that regenerator kicks in before darm comes back. Regen will heal up 33% of his health, meaning that assuming that slowbro does not get a free swap in between now and the next time you get darm in, slowbro will have around 12% prior damage, which still isn't quite enough for a 2hko, but it puts him at a much riskier position.
Cloneblazer12 Please see the previous few pages as to why simply checking a wallbreaker isn't good enough.