except glare is not the worse that Serperior can do to SalamenceImagine that I indeed kill Forretress with HP Fire, as you suggest. The next Pokemon in for my opponent is Salamence, and it holds a Lum Berry. Salamence knows that the worst Serp can do to it is Glare, which gives it a chance to get in a nice, free Dragon Dance. I'm now facing a +1/+1 Mence that forces my Serperior out, and threatens my entire team. Forretress, by comparison, has plenty of easy, hard counters and there are more than a few offensive Pokemon that can simply set up all over Forretress. I'd much rather cover Salamence with my offensive coverage than Forretress.
+2 252 SpA Serperior Dragon Pulse vs. 0 HP / 0 SpD Salamence: 308-364 (93 - 109.9%) -- 56.3% chance to OHKO