Cleon
Legend
If you're keeping it in the same place, then, how about
Capsize Boat (Ex): Silkies in seal form can capsize boats. The silkie must succeed at a Strength check against a DC of (15 + length of boat in feet?) to tip the boat over. Silkies often use Aid Another actions when attempting to capsize a boat. Any unsecured occupants or cargo in a capsized boat ends up in the water.
Capsize Boat (Ex): Silkies in seal form can capsize boats. The silkie must succeed at a Strength check against a DC of (15 + length of boat in feet?) to tip the boat over. Silkies often use Aid Another actions to help another silkie attempting to capsize a boat. Any unsecured occupants or cargo in a capsized boat ends up in the water.
Are we still omitting Pack Tactics? I briefly toyed with the idea of something like:
Pack Tactics (Ex): Silkies in seal form have an instinctive gift for coordinated effort. If a silkie in seal form uses an Aid Another action on another silkie in seal form it gives a +3 bonus instead of the usual +2.
We should probably also look up DCs from similar abilities.
EDIT: I agree with splitting the two abilities and just mentioning the skin in alternate form. I'd let a silkie go make a new magic skin in Land Under Wave, assuming it can get back. Probably an expensive ritual, though.
Let's have a go at them then:
Alternate Form (Su): A silkie can assume the form of a handsome half-elf or an unusually large seal. It must be wearing its Magic Skin (see below) to assume seal form.
Magic Sealskin (Su): All silkies possess an enchanted sealskin which allows them to assume seal form (see Alternate Form, above). Should another creature steal this skin, the silkie is unable to attack them unless the skin's thief attacks the silkie first (as per the affect of the sanctuary spell). Furthermore, the silkie has a -4 penalty to resist all Charisma-based skills and saves against enchantment spells performed by the skin-thief.
If a silkie's sealskin is destroyed, the silkie is able to create a new one by performing an hour-long ritual in the Land Below Waves with the assistance of a silkie with a magic sealskin.