There are no units that currently fit that bill,and there are not currently alliance within the 9th age realm. But if you love those models you could some how use them as other units? As long as th bases are the same size, model use is up to the user!
Welcome P L! Could you clarify the first part of your question about beast master? As for assasins, you can take as many as you want! As long as the points you’re using are within the army composition restrictions. You can see these restrictions in the army book which is free to download under the beta rules. I believe characters can be up to 40% of your total army points! Let me know if you need anything else.