Level 14 "Sleepiborough" is an annoying one because of poor design.
Technically the creature pool consists of Trolls, Warlocks, Hellhounds, Dark Mistresses, Bile Demons and Dragons.
BUT,
the level script is set up so that the following problems occur:
(1) Only the two enemy Keepers can attract Bile Demons and Dragons. To acquire these, you will have to capture them from enemies - or, at least, capture one (or transfer from a previous realm), and scavenge more from a Scavenger Room.
(2) The player cannot actually RESEARCH a Workshop, and therefore cannot attract Trolls... at first. However, there is a hidden Workshop in the bottom right corner of the map. Find this, claim it (and its inmates - including a level 10 Troll) and you will be able to build more Workshops and attract more Trolls. Beware of boulder traps on the way. If you don't get the Workshop early enough, the enemy will get all the Trolls too.
(3) This leaves you with only Warlocks, Hellhounds and Mistresses as possible recruits. And, of course, you have to research the Torture Chamber before you can get Mistresses, and the Scavenger Room before you can get Hellhounds... and by that time, you've probably already filled up your creature pool with Warlocks. In any case, you definitely don't want hellhounds - but you DO want several Mistresses. Throw back at least half your Warlocks as soon as you research the Torture Chamber, and build a big one, get yourself loads of Mistresses, train them up. Once they're high level, they're hard as nails, and can even haste themselves so they can do both your remaining research and your manufacturing, so you don't need too many Trolls either.
(4) Fortunately, you can just wait your enemies out... you can get access to gems, they can't, so just go for the gems and wall yourself in , don't be tempted by the huge gold seam to the north. Let the enemies exhaust it... and then watch their minions desert for lack of pay. Then waltz in and destroy the remains.
Level15 "Woodly Rhyme" is a trouble - you can get Dragons (but you must build a LARGE Treasury and Lair) and Warlocks, but there are no Bile Demons in the realm except one wild one, free to the first Keeper that finds him. So, make sure to research up to Barracks and Torture Chamber, and get Orcs and Mistresses. Beware the high level heroes in the lake - or hope that the one of the enemies digs into the lake first and gets killed by them.
Level 16 "Tulipscent" is a real bugger because the enemy Keeper keeps attacking you, AND there are wandering parties of high level heroes. You will have to wall them out of your dungeon and hope they break into the *enemy* dungeon - or, if you are fast enough, wall them into their Portal so they can't escape, but that leaves nothing to stop the enemy keeper attacking you with his two free level 8 Orcs (although if you're lucky one of them will die to your free Boulder trap). Meanwhile, you start with 1 Warlock and 2 Reapers, and if you build a big enough Hatchery and Lair you can get the only two Bile Demons in the pool, but until then you'll get nothing until you can build a Barracks and Workshop for Trolls and Orcs. (hint: Orcs are key, if you can get enough and train them to level 5+ so they can haste themselves.) Meanwhile, do whatever it takes to keep your Reapers training: once they hit level 5 and can haste themselves, they will turn the battle on their own. This realm I found the hardest of all the realms: but it's poor design, not bug.
Levels 17, 18, 19 and 20 have their own problems which I'm not spoiling here...
