Aquatic pvp is fairly straight forward however it is very different from land/cenozoic pvp. In aquatic pvp the battles will be faster, with class order and switching much more important. With that being said a few setup and battle tips will turn a lot of your losses into wins.
The first thing to nail down is your Dino setup. I highly recommend having one of each aquatic type in your lineup however you can also use the same class for all 3 slots.
If you are using the same class for all 3 slots then strategy is quite simple. You should order your Dino’s from highest hp/lowest attack to lowest hp/highest attack and you will never switch your Dino’s regardless of what your opponent does.
If you are using all 3 aquatic types as I highly recommend you should typically put your highest hp/lowest attack Dino first as you mentioned. However the remaining two Dino’s need to be in order of the advantage wheel. So for example if your first Dino is a cave the next two need to be reef and surface in that order. This ensures that when your opponent switches to a Dino with class advantage and kills your Dino your upcoming Dino will automatically have the advantage against their Dino.
The second thing to master is your early game strategy. The first 3 rounds will decide who wins or loses the battle nearly every time and switching is key. Any time your opponent switches to a Dino with the class advantage you have to counter and switch to your Dino with the class advantage. With the class advantage you can kill most Dino’s in two hits and nearly all in 3 hits. This is very important to remember, round 2 is the most important round as you both have the ability to land 2 or 3 hits.
In round one unless your opponent has the class advantage and can kill you in the first round, which isn’t typical but in that case immediately switch to the advantage, reserve your point. Just as importantly mentally note how many points your opponent has left. Many times the opponent will switch to a Dino with the class advantage with their first move. Remember always counter when the opponent switches.
In round two you are looking to make a kill. If your opponent has switched you counter and switch to advantage with your first point, if you can kill the opponent with your remaining one or two points do it. If you can’t kill your opponent reserve your remaining points.
Round three is dictated entirely by what happened in round two. If you killed an opponents Dino the previous round reserve all of your points. If you did not kill a Dino then counter any switches the opponent has made and kill their Dino assuming you have the points. From this point the win should be quite easy just use the minimum number of attack’s needed to kill your opponent, reserve the rest, and of course always make sure you counter switches.
TLDR: To summarize all of that in a very small nutshell just remember always keep your aquatic Dino’s in the order of the advantage wheel and always counter when your opponent switches to a Dino with the advantage. These two tips alone will allow you to win a lot of battles