Perks can be purchased from the fourth tab, labeled by a star and colored green.
All perks are inherently unlocked throughout the game regardless of whether you have prestiged or not.
They can only be purchased with diamonds and they give powerful boosts to help you advance.
Perks can also be obtained by completing Day 3 of the Daily Dungeon.
1Base cost is 100, it scales after Stage 100.
2Cost per skill is in order: 20+20+29+29+35+36, Cost doesn't change. Skill Refresh will activate for the cost on only one skill if the rest are running... and it refreshes all skills, great when you are reusing several times in a row.