You need 400 slayer points, you also need 55 crafting to make it and 20 summoning to wear it.
Remember: wearing your black mask helps kill monsters faster!
Fastest in number of tasks Edit
If you are already earning slayer points take tasks from the hardest slayer master you can, otherwise the easiest to get the "four in a row" you need to start earning.
Kuradel (for level 75 slayers with 110 combat) gives 18 pts per task plus a bonus of 90 per tenth task, and 270 on the 50th. So if you are starting out
- 10 tasks = 180
- bonus = 90
- 8 more tasks = 144
Total: 414 points
But the quickest way in tasks from 0 points is if you are just about to claim on task 43, 8 tasks= 144, bonus =270 total = 414.
If you are a lower level you will need to use the lower level slayer masters and it will take longer.
Fastest in time Edit
Depending on level it may be faster to take 9 tasks from Mazchna for 1 point each then the 10th from the highest master you can use.
Bear in mind the possibility that depriving yourself of XP this way may stop you from getting access to a higher slayer master!