During almost any event which uses Sigils you can boost your Team's Skill Points by spending more Sigils per battle. These battles are called Epic Fights and are intended to help you make more progress in events than you're normally able to.
Epic Fight Overview
Epic Fights are available in any game mode which costs Sigils per battle. This includes:
- Raid Boss
- Tower of Doom
- Class Trial
You can find the Epic Battle options on the pre-battle screen where you select your team for any of the above events.
Note: You cannot do Epic Battles in Faction Assaults because they use 1 Sigil per Delve, not 1 Sigil per battle.
The Skill Point Bonuses
The first time that you ever use an Epic Battle is free, after that it will cost extra Sigils. The higher the Skill Point Bonus, the more Sigils will be used.
The cost of each level of Epic Battle is in addition to the 1 Sigil you use to fight a normal battle.
For example if you choose a Mythic Battle you will use 1 Sigil + 4 = 5 Sigils.
Tip: Play as far through the event as you can only doing Normal battles, but when you start losing multiple times on the same battle, then consider using an Epic Fight to progress further.