Heavenly Hippoe, Gabriel and Angelic Gory appear as peons and support. Angelic Sleipnir appears as boss after enemy base is damaged. Angelic Sleipnir also appears as main threat, due to his knock back ability and averagely good status. Boss becomes especially perilous after teamed up with Gabriel and Angelic Gory. They break through player's line easily if player isn't prepared/awared.
Angelic Sleipnir has quite long range so bring Bahamut and any cats that have a longer range than 372. Player can consider to bring Artist cat as a meat shield if he is level 30+. Also choose cats who has AoE skills, good DPS and range, because player always want peons killed ASAP.
For first time:Since this is probably the first time you encountered angelic sleipnir,it is reccomended to spam any anti angel cats.Bahamut should take care of sleipnir,so dont worry about him.
Note:a true form is very useful.
For later on in the game:sleipnir isnt much of a threat anymore.Just kill him with anti angels,macho legs,crazed sexy legs,etc...