I used mainly Abaddon for almighty spells and Uriel for healing ;). Skadi was good to, but she has some major weaknesses for this part of the game. Soma's are rare to come by, I only got like three in the whole game on the dungeons, plus 2 If i'm not mistaken, from a quest.
To get Mara, you'll have to be at level 62, and you'll need Justice Throne, Sun Jatayu and Death White Rider.
Trumpeter on the other hand, you'll need to be at level 67, not 63 as I said before, sorry. He's one of the exclusive fusions, the Hexagonal fusion, and he needs these personas exclusively
Death Matador x Death White Rider x Hierophant Daisoujou x Emperor Pabilsag x Hangedman Taown x Tower Tao Tie
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
