Celestial Seas could be considered a Star Ocean 2.0, as it has a very similar concept of a boss that must be defeated quickly, or else a strong unit will become stronger and stronger, but this time with area effect instead of doge dark's single target. The stage 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.
Begin by immediately sending out a Manic Lion to fight the poens to build cash quickly. This will allow you to deploy your expensive units early enough, since they are usually slower, such as Ururun and Bahamut. When the Le'boin spawns, outrange him with Bahamut and Ururun and stall the Gabriels until the Le'boin is dead. Bringing Area Attackers is recommended against the Gabriels, as they provides reliable cash supply. Try to fight close to the enemy base, because the farther you get away, the more time it takes to get to the enemy base, which means you'll have to face stronger Gabriels. Once the Le'boin is dead, your units should be able to make a push and once you've begun attacking the base, you've essentially secured your win.
If you have Warlock and Pierre, then this stage becomes extremely easy. Just spawn a few Crazed lions at the start of the battle, upgrade your rich cat to level 2 and then spawn Warlock and Pierre, as long as you don't spawn in too many Crazed lions (or they'll bring out the Le'Boin), you will win.
Strategy 3 (few ubers with range)
Row 1: Manic Mohawk cat, Mohawk cat, Eraser cat, Crazed wall or Manic eraser, Crazed cow or Manic lion
Row 2: B.C.S tigerclaw, Divine Kalisa, King gamereon, Ururun cat, Crazed bahamut or A. bahumat (be careful with A. bahumat)
Start by sending in Crazed cow to eliminate the peons, then bring in Ururun cat ,then bring out Kalisa to help eliminate the Gabriels and bring in Gameron for help and finally Tigerclaw and Bahamut. A CPU is helpful for a stacking job, other than that keep spamming meatshields and enjoy a quick win.
Strategy 4 (ft. Kasa Jizo)
*: Research Combo M
You can bring whatever you like in the last slot, preferably Ramen Cat.
Stall the peons until Grabriels spawn, then spawn your Ubers. Keep spawning meatshields and Kasa jizos against the Le'boin and Grabiels and you'll eventually win.