Don't use Iron Tail Weavile ffs... on the subject of bad lures, there's very little point to a lure that fails a quarter of the time, imo. If you're gonna lure it, you'd better hit. No one would use EQ Latios in OU if EQ had 75% accuracy, and you shouldn't use Iron Tail here if you have another option. Use 95% accurate Metal Claw, which conveniently still does:
252 Atk Life Orb Weavile Metal Claw vs. 0 HP / 0 Def Mega Diancie: 250-296 (103.7 - 122.8%)
It's not like you're using that Steel move for much of anything but Diancie. You're generally better off using Knock Off on Azu and Kyu-B anyway. The only things you're using Iron Tail for are Gard... but Knock does a solid 70% there, and Sylveon, who should live anyway if it's EVed well (and is rare at top level).
ps Scarf Exca is a cute mon that I approve of