There are countless peppers out there in the Mexican cuisine, though we won't see most of them, though some are becoming more available, through the internet. Some can be substituted for others, but many are pretty much unique to themselves (though different regions will have different names for the same pepper). The smoked peppers are pretty much the same, though different sizes - mora, morita, meco, as well as pasilla de Oaxaca, which looks more like an ancho, that was smoked. Chile de árbol is a pepper that pretty much just adds heat, and I use my Thai peppers anywhere those are called for (or in Indian or Szechwan cooking). They are sort of like adding cayenne - basically for heat, not flavor. Not sure what pasval or pascal peppers are - maybe a company name for a peper?