Press Ctrl + Alt + C during play. You'll hear a sound to confirm. Now enter the
following codes: 

do not fear the reaper          Beat current level
feel the power                  Monsters raised to level 10
this is my church               All rooms 
fit the best                    All traps 
i believe its magic             All magic 
now the rain has gone           Full map 
show me the money               More money
ha ha thisaway ha ha thataway Increase mana 

Level select: 
Begin the game with dk2.exe -levelXXXX command line, where XXXX is a level name
from the following list:
(Ex: dk2.exe -level level10)

level1
level2
level3
level4
level5
level6a
level6b
level7
level8
level9
level10
level11a
level11b
level11c
level12
level13
level14
level15a
level15b
level16
level17
level18
level19
level20
secret1
secret2
secret3
secret4
secret5 

Not sure what to sacrifice? Here's a handy list... 

2 Warlocks      = 1 Goblin
2 Trolls        = 1 Warlock
2 Goblins       = Gold
2 Dark Elves    = 1 Troll
2 Skeletons     = 1 Dark Elf
2 Mistresses    = Punishment
2 Salamanders   = 1 Mistress
2 Bile Demons   = 1 Rogue
2 Vampires      = 1 Bile Demon
2 Rogues        = 1 Salamander
2 Black Knights = 1 Vampire
2 Dark Angels   = Gold
2 Imps          = Cheap Imp Spell
2 Fireflies     = Gold

Bile Demon, Dark Elf, Warlock   = Create Imps
Monk, Monk, Monk                = Mana Boost
Dwarf, Dwarf, Dark Mistress     = Reinforce Walls


To get the different elite creatures you have to make your room fit these patterns
following the key:

1 hatchery
2 Lair
3 Treasury
4 Library
5 Workshop
6 training room
7 guard post
8 Combat pit
9 graveyard
0 temple
! prison
@ Torture
$ Casino


Goblyn    Firefly 
121    212 
222    111 
121    212 


Warlock    Troll
24442    25552
44444    55555
44444    55555
44444    55555
24442    25552


D.Elf    Skeleton
66666    3!!!3
67776    !!!!!
67776    !!!!!
67776    !!!!!
66666    3!!!3


Mistress   Salamander
@@@@@    26662
@!!!@    66666
@!!!@    66666
@!!!@    66666
@@@@@    26662


Rogue    
3$$$3
$$$$$
$$$$$
$$$$$
3$$$3


Bile D.    B.Knight
5555555    6666666
5111115    6888886
5111115    6888886
5111115    6888886
5111115    6888886
5111115    6888886
5555555    6666666


VAMPIRE    D.Angel
4444444    3222226
4449994    3000006
4449994    3000006
4999994    3000006
4999444    3000006
4999444    3000006
4444444    3@@@@@6


*NOTE: Vampire and Dark Angel rooms must be aligned North.