Source: http://pastebin.com/ydvZHLJF

make sure your game is at the latest patch
 
attach cheat engine to darksouls2
 
click "memory view"
 
right click - display type - 4 byte decimal
 
ctrl+f, set it to search for text make the starting address 1f and search for "CHR_PARAM" exactly as i have it typed (so all caps)
 
you'll get a result, but the wrong one so search again (don't change the starting address this time)
 
now you'll be at the right one, this is what you should be looking at right now: http://i.imgur.com/RPEqBGr.png
 
so let's use a random row to define what's what -- 293200 3050 10240 293200 2235 9880 --
 
293200 is a separator, don't mess with it
3050 is the id of a creature, do not edit this or the game will crash
10240 is the creature that the game will load
293200, again a separator
2235 is the id, again don't touch
9880 is the actual spawn id
 
so 10240 and 9880 are the numbers you want to edit. simply change them to the id of the desired monster and the game will spawn that one in instead
 
note that some enemies will behave strangely or not at all. apparently there's a way to fix the ai issues but i'm retarded and can't figure it out, tho it probably has something to do with the parameters. also some enemies may be "incompatible": attempting to replace one enemy with another may result in nothing being spawned eg: replacing the halberd hollows with the looking glass knight doesn't seem to work but replacing the shaded woods ghouls does. health values may be out of whack, you should be able to fix this by editing enemy_default_logic
 
table containing monster spawn/sort ids and params that may pertain to the ai in some way (work in progress): http://a.pomf.se/ngbdle.CT