Can Dismember kill my Gloryscale Viashino after I cast Armadillo Cloak?
Your opponent can kill your creature, because he can respond to the trigger that gives it +3/+3 until end of turn. Here's the sequence of actions:


You cast Armadillo Cloak, putting it on the stack. Then the triggered ability from Gloryscale Viashino goes on the stack.


  Stack:
  
  
  triggered ability
  Armadillo Cloak
  
  
  Gloryscale Viashino is a 3/3.

Your opponent casts Dismember.


  Stack:
  
  
  Dismember
  triggered ability
  Armadillo Cloak
  
  
  Gloryscale Viashino is a 3/3.

Both players yield priority (decline to cast anything), so the top item on the stack resolves.


  Stack:
  
  
  triggered ability
  Armadillo Cloak
  
  
  Gloryscale Viashino is a -2/-2. It gets put in the graveyard for having 0 or less toughness.

Both players again yield priority, so the top item on the stack resolves. That's the triggered ability, but it doesn't do anything because Gloryscale Viashino is no longer in play.


  Stack:
  
  
  Armadillo Cloak
  

Both players again yield priority, so the top item on the stack resolves - or would resolve, except that it's a spell with an illegal target, so instead Armadillo Cloak gets countered.




For educational purposes, here's what could happen if your opponent cast Dismember at the wrong time (for him):


You cast Armadillo Cloak, putting it on the stack. Then the triggered ability from Gloryscale Viashino goes on the stack.


  Stack:
  
  
  triggered ability
  Armadillo Cloak
  
  
  Gloryscale Viashino is a 3/3.

Both players yield priority, so the top item on the stack resolves. This is the triggered ability which pumps the Viashino.


  Stack:
  
  
  Armadillo Cloak
  
  
  Gloryscale Viashino is a 6/6.

Your opponent casts Dismember.


  Stack:
  
  
  Dismember
  Armadillo Cloak
  
  
  Gloryscale Viashino is a 6/6.

Both players yield priority, so the top item on the stack resolves.


  Stack:
  
  
  Armadillo Cloak
  
  
  Gloryscale Viashino is a 1/1.

Both players again yield priority, so the top item on the stack resolves. This time, the target of Armadillo Cloak is still legal, so it resolves as normal.