Hiya
Converting should go by what I call the "Common Language Conversion Method". Basically, pretend that you read the special ability / spell / skill / whatever in your game system of choice (HARP in our case)...but it didn't have any specifics. What would you do, as GM, in that situation? Easy. You'd take the 'gist' of what it was probably intending, and figure out how to get that point accross in the rules.
As an example, the Ankheg D20's "Improved Grapple" as mentioned above. Well, the intent is that this creature be really good at grapleing. So, I'd simply give it a bigger bonus to Grapple attack, and maybe have it count as one size 'larger' for Critical maxiums purpose. That should do it. No need to try and equate 1:1 conversion of abilities, skills, numbers (especially numbers), etc.
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Exactly what I was aiming at..
The problem lies in keeping consistency between the monsters.
You
could simply give additional bonuses to this or that stat or skill or spell, or grant a Blood magic spell as part of the race, etc, but keeping the consistency in encounters is the hard part.
The fact that a group of 6 skeletons can TPK a 4th level group of experienced players is an example of this. DND'ers would balk at such an 'easy' fight but in HARP it is deadly to the extreme.
HARP players (and indeed ICE players) dont need a constantly evolving group of monsters with ever increasing stats to keep them occupied. Simply add 1 to a group and then get the PC to deal with splitting their parry and its a REAL challenge. (unlike the DnD method of combat).
Thats one reason I like ICE games so much - the Combat is a lot more realistic(as realistic as being thumped by an animated skeleton can get, anyway
).
Adding an armour bonus (especially if using HnS rules) or a +10 to OB, or extra range on a weapon (and thus increased point blank range) makes a HUGE difference in a combat. The differences in the game system is what makes it such a great game.
Add the Critical charts and it just becomes fun to the extreme - both defeating bad Guys (BG) and being defeated by such.
Add a spell (blood magic) ability to a creature and it really makes a huge difference. In DnD terms it would increase the CR by at least 2 - most likely 3. And that is just for the one ability.
The problem I see with CLCM is trying to understand what is a game mechanic description and what is simply flavour text. I've seen huge arguments with discussions over a creature in DnD and the Harp conversion. Eventually I managed ot get i with "this is My creature designed explicitly for my game world - the DnD monster you know simply looks like this and may be called the same name for ease of use."
Trying to separate DnD'ers from DnD is a lot harder if you start converting DnD monsters. Use new ones (M:AFG is good) and suprise them!