[Farling]

It is a specific modifier added by Deathsnatcher, since choosing another form for monstrous physique doesn't add the +4 untyped bonus.

It is the "Greater Magic Weapon" effect that is being applied directly by the race (caster level/4), since it is a "constant" effect, based on the race's spell-like ability caster level of 18. (It affects both attack and damage.)

It is probably a bug that it is automatically granting this ability when you choose this race for polymorph, since I don't think you are supposed to get the spell-like abilities of the form you are taking.

Note that the script for the race makes reference to "greater magic fang", even though the official published race has a constant "greater magic weapon" active which of course, can't be applied to natural weapons.

The script is also applying it as an "untyped" bonus, when both the magic fang and magic weapon spells provide an "enhancement" bonus to the weapons.

The script is also permanently providing a "Shield of Faith" effect (deflection bonus to AC), based on the hero's hit dice (HD/6+2, max 5).

(All this is done in eval script #2 on the rDeathsnatcher race in Bestiary 6.)

It also looks like an innate skill bonus of +19 is being applied to various skills (eval script #1), but this isn't coming across as part of your polymorph.