I'm inclined to go to 1d8, but I guess the low damage of the original monster means something. We should probably stick to 1d6. At least it can get a lot of attacks!
Sounds good. Updated.
The sickles deal an additional 1d6 over each slam, right? Isn't that better?
You know, the constriction was originally quite strong and tied to its tail. I think we should keep it high damage, and use one of those "transfer to the tail" mechanics I've seen used before. The search begins...
*SNIP*
Improved Grab (Ex): To use this ability, a marl must hit with a slam attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and on its next turn can transfer a grabbed opponent to its constricting tail.
Constricting Tail (Ex): A marl can transfer grabbed victims from a slam to its tail as a move action. Although it lacks a tail slap attack, it can constrict with its powerful tail, dealing 6d6(?) points of damage with a successful grapple check.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.