I happen to play both LM and DE as my main armies, so i might have some insight here
1) Hydras are nasty, and cheap. Even chammo skinks will not do the trick, since only 25% of their shots will get through the 4+ AS and 4+ regen. you will need to either keep it busy with a block of sauri or your equivalent of the "unkillable dredlord" (oldblood with 1+ AS, 4+ ward, stubborn and a great weapon). Both options cost way more than the hydra, and this is a loss you will have to bear. If you use magic buffs you can easily create a unit that is tough enough to grind down a hydra. kroxigors and stegadon(ancient) are options too. If all that fails, anything with the flaming banner, or a slann with fire magic makes short work of it.
2) their "unkillable" roadblock dredlord WILL keep one unit busy for a whole battle. he costs almost 300 points, and if you charge him with a normal skink cohort, he will not have time to grind it down. you have now bogged down his 300 point unit with a 100 point skink unit!. As mentioned above, remember that a scar vet with 1+ rerollable save and 4+ ward is actually MORE durable against S3 and S4 attacks. You can do the ame trick against him!
3) magic:
His magic is nasty as hell, but you can have one just as nasty. Lore of fire can actually be worth it here, since DE HATES to lose models. Direct damage will really hurt their small and expensive units. Remember that your slann can force him to ignore all 6s rolled with magic. that is a HUGE gimp
4) cavalry:
your cavalry is just as good, and still few ppl use it. Cavalry is not much to fear tbh. Sauri will beat them in the long run.
As a DE player i am incredibly afraid of all fighting units. i want to keep them at arms length and bombard them with magic and missiles before i swoop in for the kill. You can one-punch-KO him if you just keep barrelling forward. Use skinks to prevent him from slipping away and force him to fight your (preferably magically enhanced) sauri. he will NOT like that.
best of luck! (not if you ever play me though)
