Been really thinking about how to do all this.
I was unsatisfied with the Mummies being needed to boost the skeletons. So I think I'll give that scream/stun ability to the Mummies instead. Thank you Daith for the idea.
I'm thinking it'll only last one round, and I'll make it so the Mummy either needs to cause physical damage or take damage to use the scream again. That way I can't just spam it.
They only have 2 body points, so I don't think it'll be an issue. I don't want to make the monsters to annoying or difficult. Just a bit more.
Skeletons I think I'll have it where if there is only one or two left, they can also do a scream, but this scream will bring back some of the skeletons already defeated. I won't boost their stats at all, so it should keep them fairly easy to take out. I'm thinking of having myself roll a red die a lot. Maybe like 1 or 2 no Skeletons come back, 3 or 4 one skeleton comes back, 5 will be two skeletons, 6 will be three or more. So there is a chance he can bring all his friends back.
Zombies will indeed come back as Crazed Zombies. I'll give them one extra body point and the ability to attack twice.
I like this idea because it should add some more strategy to the battles. Like do you go take out the mummy first to avoid the scream, or do you want to kill the skeletons first?
I'm also going to add another new potion type to the Return of the Witch Lord quest. I think I'll have 500 gold purchasable bottles of Holy Water. Using one will give you an extra attack against undead for as long as you see undead. (Not just monsters only undead types) Also anything killed with a weapon with holy water will stay dead. So they can make it so the zombies can't come back, or the skeletons. I think I'll just have the Spirit Blade be able to do this naturally, though I think I'll let the holy water still affect it. This gives them something to grind money for. As currently they don't have any use for it as they bought all the weapons they wanted. (And for some reason no one wants a tool kit)
I'll keep the warmth bottles in the treasure, but they'll be lesser holy water bottles. They can keep it so the undead don't come back, but you don't get the plus combat dice bonus.
Since I have Femirs for the Keller's Keep quest, I think I'll add something to this one. I don't actually have Mouse Trap to add giant rats. (Or anything I could use for giant rats) so instead I'm thinking of adding a treasure type of monster, and adding that to the Femirs.
Basically the Femir will have one spell it can cast, and if it gets an attack off it can cast the spell again. (sorta like the Mummy shout)
In the Return of witchy lord. I'll re-use the ice gremlins as regular gremlins. Or Treasure Gremlins. They'll very obviously have a small treasure chest, and run away if they see you. If you can kill it before it gets away, you get it's treasure.
For Femirs, I'll have it you find a treasure on it when you kill it.
I'll have my players roll a 1d6 and depending on what they roll is the reward they get.
1 or 2 you get nothing. 3 you get 50 gold. 4 you get either the anidote if Keller's keep, or the Holy water if Return OTWL. 5 will get you a Great Potion which I'll say heals for five points of damage, and this will be the only way to get them. 6 will get you a unique treasure.
For Keller's Keep and the Femirs, I'm thinking you can get a ring of anti-poison. (There will only be one of these you can get) For ROTWL you can get a helmet but it's a 'Clarity Helm" which can block the Mummy cry from working. (again only one can be found.)
Then for fun I'm kinda thinking of adding character specific artifacts. Like a gem for the bard that lets him charm female orcs. (since I have those figures) I think he can choose to either have them all surrender and leave, or maybe charm just one to fight on their side. Would probably have to make it so the thing can only be used once per quest, or maybe he can spend a turn focusing and re-charge it, but that takes up an entire turn to do. That's probably the better option.
I'm sorta thinking of having an Axe for the Drawf. Our Drawf refuses to buy a crossbow, so he can't range attack. I'm thinking of giving him a magic axe that can be thrown forward and it'll come back to him. I'd just need some limits. For one he can't toss it diagonally. I also think I'll limit how far it can be thrown. Like maybe 8 spaces total. Or even six. It can also hurt his friends if they are in the way, as that just seems fair.
Actually maybe it will depend on a dice roll how far it can go and I'll let people dodge it if they are on his team. The main idea is to give him a ranged weapon, but I don't want it overpowered. Just so he's not stuck outside the room doing nothing because everyone is hogging the door.
Finally for the Vampire, I'm trying to figure out if they should be able to re-gain life in anyway given they are a 'vampire'
I've thought about them gaining one body point back for each successful physical attack they do, but I fear that might end up making them too strong. So I'm also thinking that maybe they can sacrifice a monster (by touching it) and either re-gaining their life, or maybe refill their spells. One or the other, but only once. They can't do one then the other next round.
Obviously I'm still playing around with things, but I think most of this sounds solid.