What does GOAT or ‘GOATing’ mean

You are right that sink and float isn't used in a lot of skills, there are some benefits I've noticed however that make the skills bestowing the effects worth of using:

• As was noted in the comment by Lyrion: Sink keeps the enemy (players mostly) from swimming to the surface to rez.

• Both skills can be used as means of crowd control, either pulling or pushing enemies away from you. This makes it possible to keep melees from beating on you or taking ranged enemies closer to your melee range.

• Both skills can be used to move an enemy into or through an aoe damage area. The first example I can think of is the elementalist using: lightning cage and then Air Bubble, pulling the enemy through the cage. Otherwise, enemies aren't inclined to touch the cage and get stunned.

• When fighting multiple enemies, you can catch the enemy in a Sink/Float effect to take them temporarily out of the fight, giving time for an escape or taking less damage for a small time

1. You can work on the holiday achievements, if you haven't completed them all. (Emissary, attend the party, and mad king's world are the only ones that can't be completed in act 3, I believe.)
2. You can do Halloween crafting: A. Food and tonics B. Halloween exotics (very expensive, though)
3. You can trade candy corn to trick-or-treaters in LA for personalized trick-or-treat bags, and try to get an endless tonic or other rare item.
4. You can play costume brawl (this will still be around after the event, but I suspect fewer people will be playing, at least til we get Wintersday costumes.)
5. Wait and see what's in store for act 4.

Also, in addition to the costumes in te gem store, there is a pack of Halloween mini-pets. There is also a fourth pet that can only be obtained by putting the others into the mystic forge.