I really like playing AoE 2 DE, BUT getting sick and tired of Mangonels.
My goal is to have large armies battling each other, hence 3 Mangonels taking out 150 man (swordman, archers etc) at short range ruins this concept.
Is there any mod available to disable them from being build (obviously outside multiplayer)?
You might say a siege onager can kill 30 units at the same time, but 150 units? Are you using the x256 mod?
Well, then you should learn to find counters. The best Counter to Mangonel is cavalry.
For Siege Onager, you might want to use Bombard Cannons.
It is possible to modify standard AI, so that it doesn’t research/train them, but I don’t know exactly how to do it.
In scenarios you can disable mangonel technology.
I don’t mean 150 at once, but within a very short time.
Of course, I understand I can build cavalry, but I do love massive battles with normal units as well.
Where can I disable that? 
More exactly it seems, that you need to disable mangonel-line units. You need to do this for each player. Disabling siege workshop building would also work I guess.
I think CBA scenario will be to your liking.
