If you're facing the genies/Outraging dragons, then you need Ice Shard for priority, no doubt. But when it comes to Icicle Spear or Crash, I reckon Icicle Spear is the one to use. In terms of simple power, three hits gives you 75BP, not too far behind Crash, and of course you can get 100BP or 125BP from it too. Variable power and the loss of flinch isn't such a bad trade off for the pluses of Spear. 100% accuracy is a major, major plus too. But breaking Subs is the real killer. The ability to switch into a Subbing Dragonite, Gliscor or even Breloom (if you're brave), and then KO it straight through, is invaluable. I've been in situations where I've tried to status a Dragonite, but been blocked by its Sub, switched to Mamo as it Roosted - then KO'd through Sub AND Multiscale (with 4-5 hits of course). Five hits and some luck, and you can 'OHKO' Donphan through Sturdy, preventing rocks or a spin. Ice Shard and Icicle Spear makes Mamo a kind of 'utility attacker'.