I have a friend who plays chaos marines. We ran a game of 7th where she used a sorcerer based demon factory. I play Tau. The match started off looking like a standard game of
40k 7th edition. I went first and did some piss poor rolling to damage her predator and vindicator. Night fighting was in effect so everybody had stealth, which later became useful to me in her shooting phase as my fire warriors got 3+ cover saves in a terrain base aegis line. She moved her raider up and dumped her Sorcerer
IC cluster

into cover behind a ruin. She then proceeded to use a dice cube and then some to summon Tzeentch heralds and two squads of demons, against my one deny dice, which failed when I tried to use it. She managed to point my apc once, and killed two fire warriors due to night fighting and cover saves. The phase switched to me and I readjusted my troops and damaged one of her preds again while failing to damage her vindicator due to

dice rolls. Of course my command squad didn't show up (I rolled TBV as a warlord trait without re-rolling) which didn't help what happened next. She had to open another dice cube and began spamming more demons. This was the last turn we had enough models and that was using proxy cultists. She marched on me and began an advance with her land raider, pointing my apc another time with a weapon destroyed result taken against the burst cannon. She pointed my tank once too. My turn came and my troops got shooting at demons or retreating depending on the proximity of the enemy demons. I damaged her predator again, and rolled

trying to shoot the vindicator with my broadside squad. Commander failed to show up again. My friend took her movement phase. She then proceeded to borrow my dice and we used some pre-prepared cardboard base proxies for her demon army she summoned. In one turn we burned through 50 of the 60 cardboard bases I had brought just for this. Shooting was done and my apc escaped death narrowly (cover saved 2 penning shots off of lascannons). My commander finally stopped

around and came to the table and I fell back on my left side hard. I wrecked her predator and failed again to damage her vindicator despite the metric

of dice I threw at it. My command squad wrecked a squad of demons entirely and then jumped out of assault distance. Her turn began and we got out more of her dice and mine and pulled out the shops models to borrow for the

that hit the table despite the fact I denied one of five summons. Some of what hit was blood crushers too, which she took wounds on some poor nerglings to summon (Tzeentch is a

to Nurgle). My left flanked died badly to shooting/assault and the demons were in my face. My remaining army shot apart about two squads of demons, only to be assaulted by 5 squads at once on my friends turn. Game ended and she won in terms of
VP.
We barely had enough proxy to play that game, at 1500 points. That is including the store models and my cardboard proxy bases. Half the table (6*4) was coated in demons. Malefic summoning is broken to any faction that can reroll its warp dice at this time, further broken by the fact my friend could only peril on double sixes due to a demon upgrade for her sorcerers. I don't want to remove Malefic powers from play as of yet and I don't want to nerf the ability of chaos factions to reliably spam other psychic powers. The question is what house rule I can use to balance this and prevent the absolute

that was my last game. My friend actually felt bad for cheesing me like that, and she used to run drake spam which was tolerably due to it being one of few competitive chaos builds!
PS: It took over 4 hours to play.