1. DT:M
2. Raid

Here's the example of my main Raid Deck during the event "The Frozen Land" :

The deck in action :


The thing is to overbuff Asuka (and Blaze) to deal big amount of damages with normal hits.
In my opinion, it is way better to try to overbuff cards with high attack against raid bosses than trying to use multiple damage skills.
Here, Asuka & Blaze often do ~3M damages with their normal attack (not counting skills) and can stand multiple rounds (2).
Asuka will be, at every fight 7x buffed (from 1x herself, 2x Genzo, 1x Captain Fiene, 1x Reina, 1x Sect, 1x Beginner Ema) and can be, at max, 10x buffed (1 more from Genzo, 1 more from Reina, 1 more from Blaze), which makes her deals from 3M to 6M damages (on red bosses, actually).
This is the same thing for Blaze, but she has less buffs (from 6 to 8)
I used Candy here because during the "The Frozen Land" event, she had 2x points bonus.
NB : My cards were all fully-awakened and almost maxed-skills. Asuka +1, Captain Fiene +1, Sect +1, Genzo +19, Blaze +20, Reina +2, Beginner Ema +7. My Beginner Ema also had 4th skill : Fang of Death -Beginner-

Here's the example of how I try to kill, with the lowest spirit cost I can (actually 16 is my min), Warrior URs bosses from the event "The Ice Demon"
I first use the Free Attack and 2 Standard Attack (8 Spirit) with a debuff deck :

And when I encounter this boss another time I do two Standard Attack (8 Spirit) to kill it (because of turn limit) with a dps archer deck :

Here's the video after 3 debuffs :


Edit : I tweaked my archer deck so I do actually need only 1 Standard Attack (against Vanessa lv 14) :

The goal here is to debuff the boss enough in order to make your dps deck able to stand multiple turns before getting killed.