I set a adhesion trap hole to counter if/when my opponent uses his vanguard of dragons ability to special summon blue eyes... but it didn't activate. Does anyone know why? I was under the impression that it didn't matter what kind of summon the opponent does...
This just happened to me today which is why I came to this page to find an answer, for some reason it didn't work when my opponent used kidmodo to summon Blue-Eyes
The times you can't do it are pretty simple. The Summon has to happen outside the Damage Step (since cards like Floodgate Trap Hole are Normal Traps, which normally can't be activated there), and the Summon has to be the last thing to have happened. (So the Summon effect can't be Chain Link 2 or higher, or do something after the Summon, such as Trojan Gladiator Beast's draw.)