Angelic Sleipnir has quite long range so bring Bahamut and any other Cats that have a longer range than 372. Consider bringing Artist Cat as a meatshield (if he is Level 30+). Also, choose Cats with Area Attacks, good DPS, and enough range for Sleipnir, because you always want those peons killed ASAP while keeping Sleipnir from killing you.
For new players: Since this is probably the first time you've encountered Angelic Sleipnir, it is recommended to spam any Anti-Angel Cats. Bahamut should take care of Sleipnir, so don't worry about him. Also, any True Form is recommended, especially The Flying Cat.
Strategy 1[]
Lineup
Notes: Use the remaining slots for any units of your choice.
Notes: Use the remaining slots for any units of your choice.
Stall the three Heavnely Hippoes with Ramen Cats and, when Angelic Gory comes, start spamming everything EXCEPT Awakened Bahamut. When the enemy base is about to get damaged, send Awakened Bahamut and fire the Cat Cannon when he hits the base. If done correctly, Bahamut should attack the base and the boss once. It will be knocked back but since you have supports behind the line, they will kill the Angelic Gories and Heavenly Hippoes. If you are lucky enough, Bahamut will run through everything and hit Angelic Sleipnir. A level 30 A. Bahamut can take Angelic Sleipnir in a total of 4 hits. Leaving him just 1 knockback left to kill the boss.