Quoting me here...
Things like Tzeentch armies of old relied on the fact that every unit of horrors shot fireballs. The trouble seems to be stemming from people claiming an army had a very very large amount of dice and used to make more units for more dice. But as I have said in several threads (including this one I think), that if you are spending all your dice on making new units you aren't killing anyone with them. It would be like having a fully loaded predator / vindicator / leman russ and choosing not to fire the gun because you prefer tank shocking everything.
If you threw this example at another army it would say be a guard army. You have chosen to give up all those lasguns, heavy weapon supports so in essence sacrificed all your shooting with all your guns and replaced them with walky talkys (E.T. reference there)... but you can get 25% pts of guardsmen each turn, or unarmed guardsmen who can also help summon more.
Sure you will have mass numbers at the end of the battle potentially, but the likely chance is your enemy has actually caused more damage to you than you can summon, and because you aren't doing any damage to him they will win the game of attrition. Not to mention that just having loads of models doesn't always net you objectives and there seems to be a load more of them now.
In effect the Tzeentch fireballing army is heavily nurfed because your chance to actually cast your spells used to be over 91% pass rate regardless of using flickering fire at WC 3. NOW casting the same spell if left to just the dice they generate themselves they will only succeed 14% of the time...
If you go for the WC3 version and you add 2 dice from your spare pool it goes up to 50%, add another dice an it is 66%, but that is burning a whole secondary units power to cast a spell that in 6th you could have had 82% to cast both, and 99.19% to have just cast 1 of the 2 between them.
Of course the deny the witch thing is slightly different as well, and rather than just needing the one roll of 5+/6+ that they could roll regardless. They now have to manage the dice they have to try to roll enough 5+/6+ rolls to stop the spell. So on mass casting with loads of dice, unless your opponent also has loads you should get loads going through.
So yeah as everyone is pointing out, yeah they can summon armies from armies who summon armies... But actually the chance is low and the models you make are delayed in actually taking part in the battle as they deep strike so cant charge on that turn.
Here's the kicker, that's just primaris malefic spell, you can continue to summon blood crushers, screamers, or seekers
Isn't it Hounds, Flamers, Nurglings & Seekers? or has it changed since the posting of the cards on this forum by Zion here https://www.heresy-online.net/forums/...&postcount=492