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Deals damage and has a 100% chance to lower the target's Speed by one stage.
This is the signature move of Kyurem, but the frozen dragon probably hoped for something better. It's weak enough for the side effect to be almost neglected by the majority of competitive players. Finally, remember that the last piece of the Tao trio can make better use of his brilliant offensive stats using the much more powerful Ice Beam or Blizzard.
However, if you want to employ the surprise factor (and your predictions skills are accurate) this move can be useful. The idea is to use Kyurem as a bait to their counters; use Glaciate on an obvious switch and proceed to make use of Kyurem's adequate coverage options while the opponent has reduced Speed.
Ice Beam is a stronger alternative without a secondary effect.
Icy Wind is a less powerful equivalent.
Electroweb is a less powerful Electric-type equivalent.