Originally Posted by Fat Blitzenith
Why is Screech never used on Tyranitar? It halves defense, right? So that's basically a Swords Dance, albeit with only an 85% chance of succeeding. Couldn't it also be used as a psuedo-phazing move?
Well, debuffs in general aren't too powerful to begin with.
First: -2 is not
the negetive equivalant of +2. That's because buffs increase your stats proportional to your current value ...
150%, 200%, 250%, 300%, ..., [stage] * [value]/2
... while debuffs get weaker with every stage the target descend.
66.6%, 50%, 40%, 33.3%, ..., 1/([stage] * [value]/2)
For example: When using Swords Dance or Nasty Plot, you double your attack stats. When you now compare to Screech and Fake Tears, they only strip your target of 50% of their defence. That's not said, that debuffs can be inconsistent for another reason: Your target is not definite unless it is the last Pokemon - your opponents have more control over the situation because they can decide on which Pokemon receives the debuff. If the Pokemon's defence happens to be low, Screech even turns out to be weaker than it already is.
Tyranitar isn't even good at using debuffs for pressure; it's so slow that it won't force out anything soon, especially because it doesn't have any priority moves.
There had been a few Screech-Flygons last generation, when Salamence was uber. The main target was Skarmory, but now that Salami is back it just should use Fire Blast.