[Ancalagon]

If you want to avoid night goblins just because you don't like the models you could always use regular goblin models for some and convert things like fanatics and squig hoppers to look like common goblins. That's if you wanted such units in your army of course. A few orc units usually helps, particularly on the leadership front, but this is less important with regular goblins than night gobbos since the regular goblins have a higher Ld anyway.

An all goblin list is certainly legal. Just as long as you've got a general and your minimum number of core units you're good to go.