1 - Angra Mantis only works for thief class. See part 4.*
2 - Luminous Blue Light Stone is better than Perverse Demon Mask since it gives 22% crit dmg and 3% reduce after cast delay wont do much. If you are worried about the high def monsters, just use a Thanatos instead of 2 True Seyren cards.
3 - Gambler Seal and HPM set gives 13% higher crit dmg than Mob scarf combo but you will lose HP, 18% atk, some variable cast time and a slot. Both are good and is up to you to decide what you want.
4 - Deep Sea Merman Card is a better option for Boots slot. It gives +4 atk per 15 base STR and 15% crit dmg if Sea King Dramon is equiped (head slot)*. Sea King Dramon is a weaker version of Violent Coelacanth card and also reduces your HP by 5%.
5 - A +16 Temporal LUK Manteau gives 24% crit dmg and is not cheap. It gives 7% atk bonus but i dont know if gives you a better dmg in the end. You can get 32% crit dmg with a +9 FAW and also a bit of raw atk and some Neutral resitance.