The "Rules Questions" thread would be a better place for this.
Originally Posted by Zvendels
Now we start placing monsters, we all place goblins and undead, in the end there are about 20 monsters and Xykon has 54 in attack and defense!
Keep in mind this rule change from the FAQ:
Any given monster that could provide support to more than one other monster only actually does provide support the topmost monster in any given room.
So for example, if you play a Goblin Necromancer, with its own Horde Support from Undead monsters, any Undead monsters on the floor would support only Xykon, since he's on top, not the Necromancer. So the Undeads trigger only one Horde effect, not two. It's still possible to get some pretty big stacks even with this rule change, but it's less common.
The only way I can see that can possibly defeat him is "I forgot they could to this" card, if it works on support abilities, which I'm not sure off.
Yes, you can do that. It would only apply to one of the support effects, though, so you can use it to eliminate either Horde (if you do it before the extra monsters are added) or Assist (probably a better idea).