Sky Castle Finals is every Sunday 9 P.M Server Time. For me its the most important event as ranking 1 to 3 guarantees a gold dragon ball. The 4th or 5th Gold Dragon Ball gives 8k to 20k BR Each so getting 2 guarantees about 15-35k additional br for about 3 days. They also give huge amount of sky medals when you dismantle them allowing you to purchase more Dragon Balls.
My strategy to rank high is plain and simple, I hit both towers and enemies at the same time. that way, its like hitting 2 birds in 1 stone as both are accounted in the pointing system. Its very rare that I kill an enemy walking alone unless they are dying. Melee jobs are at great disadvantage because you will really receive the tower damage when attacking. FW are the best jobs for Sky Castle Finals IMHO.
Also, note that damaging an enemy is counted as KILL when they die within 20 seconds after hitting them, so flock at the area with the most enemies, do some damage and run the hell out of there to find another flock of enemy you can damage. This principle is exactly the same in GW wherein, you only need to hit enemies and you get the kill when they die so to rank 1 in GW, just AOE that shit out of the enemies, the more you hit, the more assist = kills.
To further maximize gains, Get Khal Drogo Card and leave the AOE in their tower or on area where there are lots of people dying, everyone that be damaged and die afterwards will be counted as your kill.
and BTW, assassin artifact skill sucks.