Reins of the Crimson Water Strider is the same kind of water mount as Reins of the Azure Water Strider in MOP, but it has a different color. To get the Crimson Water Strider, you must be well prepared:
1. You must build a Fishing Shack in your Garrison and advance it to level 3. In order to unlock the level 3 Fishing Shack, you need to fish seven different Enormous fishes each kind with 100 fishes to gain achievement Draenor Angler, and get follower Nat Pagle as well.
2. You must become Best Friends with Nat Pagle. It requires to Best Friends with Nat Pagle use the Crimson Water Strider while buying the mount if earned Honored status with the Nat Pagle.
3. You must obtain 100 of Nat's Lucky Coins. After Nat Pagle started work in Fishing Shack, you have to fish up "Lunkers", which are rare variants on regular Draenor zone fish, and turn them into Nat, to get Nat's Lucky Coins. Totally you need to fish up 100 "Lunkers". As the "Lunkers" can increase 400 rep points of Nat Pagle, it needs around 80 "lunkers" to turn in rep from Stranger to Best Friends. It means you will earn exalted rep when finished collecting 100 Coins.
The "Lunkers" is related to the fishing skill points, the higher fishing skill points, the higher drop rate of "Lunkers". That is to say, increasing fishing skill will help fast get the Crimson Water Strider.