yes it WOULD work if he had anything else going, but check his list. he has no punching power at all. he has three units all of whom will lose or at best tie with our saurus blocks. hence you can lock down his army with your army and make sure you win in one place and not lose in the other two.
i am not saying point denial never works, but in this case you can actually score points off him while losing none yourself. Buying a unit or two of 20 zombies and raise them more or less accidentally during the battle will be a great speedbump, but putting basically all of your army into two huge blocks of the worst unit in the game and then being kind enough to deploy it as a horde so you can rip through it very fast is pretty much just handing over the victory. yes he has tied up your two main combat units (TG and stegadon in this case) for a few rounds of combat, but he has no units that can capitalize on this. Had the crypt horror unit been bigger (maybe 8-10) they could actually have ground down a saurus block in time to help, but as is, with only 6 of them (and hopefully skinks and salamanders will keep that lower) they will also just act as a speedbump.
Every one made this misjudgment when 8th edition came out, and figured "hey, skavenslaves costs nothing. i can buy several units of 100 of them and with steadfast they will never flee!" then we started to realize "ok, so skavenslaves never flee, but neither do they ever win". Cheap tarpit units can keep you from losing a game, but they will not help you win it. 100 zombies are still zombies. yes they will stand for a while but they will never ever win a round of combat. you need punchy units too so that you can tie up key units for a few rounds while killing other units elsewhere. this particular army has no such units. he can hold and not die for a few rounds but thats it. he can not actually win unless you give him points in the form of skink units and such. this is why it is important to quickly get rid of the ethereals so they cant kill the skinks. if you let this happen THEN you might lose, but as long as you stay nimble and crush his small units fast you should have no problems.
Oh and has been mentioned you must naturally have a slann with becalming for this to work. curse of teh years has a short range, so if manfred wants to cast it he will have to enter the slanns 24" bubble. his magic phase will be really crippled by this. he cant chuck loads of dice into a single spell, cause then he will most likely "waste" a bunch of them since they are 6s. Neither can he be sure to get spells off with only 1-2 dice since the removal of a 6 can easily cause him ro get a natural 1-2 thus ending his phase (for manfred).
