This doesn't work as it is. Call Lightning doesn't kill Shadeflicker and Shadeflicker's next attack kills my Hydraling every single time. To make this work, since Shadeflicker uses his Phase when you use your Tail Slap, I passed on the tail slap all together and used Call Lightning instead when his Phase came off CD
This battle is a bit RNG and requires three conditions to win:
1. Your first pet must be faster than the enemy. Strat won't work in any case otherwise.
2. Your crab must be able to hit with blood in the water. In other words, the crab must not die until it plays all of its turns.
3. Your hydraling must not die in all the combat, as she will be the last pet alive to win it.
If any of the conditions fails to met, you should restart the combat.
I had a hard time with this. My crabs kept dying before being able to use blood in the water.
Instead I used a hermit crab with fish slap, bubble, whirlpool.
Used whirlpool, bubble, fish slap until whirlpool was back up and used that once more before dying on the switch.
Couple notes: This strat is dependent on your hydraling NOT dying in Turn 4, when Shadeflicker uses void gate to swap in the Crab. Also, the listed aquatic S/S variants for the Mongoose (all are 325 speed) will NOT work! Only the Mongoose S/S (374) and, as a previous comment said, the P/S Mongoose (338) will beat Shadeflicker's 325 speed!
Also, I did not have a P/P Frostshell Pincher. I tried using a P/P Fen Crab which, according to another comment here with the Pincer's stats, has the same stats. The P/P Fen Crab was getting killed in Turn 5, before getting Blood in the Water off.
I tried using Chuck/Muckbreath (B/B) but their hp was 1481, which was higher than the Hydraling's 1465hp, so they did not work. I ended up using a P/B Coralback Fiddler (1384/305/273) and that worked on the first try.