Yiazmat is very easy, just put Yagryu Darkblades in your three characters, genji gloves on your main attacker, and other agility boosters on your other characters, and you'll be hitting him for 9999 damage at first, then 6999 damage, x6 or x7 in each turn.
I won the fight against him in less than 2 hours and a half and only had to run away to heal once.
Omega Mark II was kinda easy, the EU version had his HP as the Jap version 10M HP. Just Decoy, Reverse, Rinse, Repeat.
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"
