Celestial Seas uses a fairly small sized map, and begins by spamming out a massive amount of Those Guys and Doges. After a minute or so passes, Gabriel spawns will begin. The Gabriel spawns in Celestial Seas are infinite, and will increase in strength every 30 or so seconds. It's highly recommended to attack the base before the Gabriel spawns begin, because eventually, the Gabriel spawns will be increased to 2000% magnification and will be essentially impossible to stall. When the base reaches 90% HP(270k or lower), a 10,000% Le'boin will spawn. The challenge will come from quickly spawning and defeating the enemy Le'boin as well as destroying the enemy base before the 2000% Gabriel spawns begin.
Many strategies for this stage will begin by, almost immediately, sending out a Manic Lion to fight the Those Guys and Doges to build cash as quickly as possible. This will allow you to get out your expensive units out first since they are usually slower movement speed, such as Ururun and Bahamut. Get as much money as you can as fast as possible and use Manic Lions to spawn the Le'boin quickly. Outrange him with Bahamut and Ururun and stall for your life against the Gabriels until the Le'boin is dead. Bringing strong Area Attackers is recommended because of the Gabriels , as they will keep your cash supply flowing pretty strong once you've attacked the enemy base. Do your absolute best to fight as close to the enemy base as possible, because the farther you get away, the more time it will take to get to the enemy base when Le'boin dies, which means the chances of hitting the timer and 2000% Gabriels spawning increases. Once the Le'boin is dead, your AoE attackers and Ururun+Bahamut should all be able to make a small push to the enemy base and once you've begun attacking it, you've essentially secured your win.
If you have Warlock and Pierre this stage is extremely easy, just spawn a few crazed lions at the start of the battle, upgrade your rich cat to level 2 and then spawn in Warlock and Pierre, as long as you don't spawn in too many crazed lions and they bring out the Gabriels and Le'Boin you will win.