All Characters start with +10% Chance to do a Critical Hit for +50% DMG. This shows on your screen as Purple Numbers. on average, 1 out of 10 hits will be a Crit.
Crit Chance: the Cap for Crit Chance is +60%. so you can improve your Crit Chance to be 6 out of 10 hits to be a Crit, on average.
Crit DMG: the Cap for Crit DMG is +350%. the +50% you start with is not counted towards the Cap, but is added to the total. so your max Crit DMG would be +400%.
Deadly Strike: gives you a chance to double your Critical Hit DMG when you get a Critical Hit. if you don’t have Deadly Strike on your Equipment, you can’t double your Crit DMG.
Deadly Strike has a +60% Cap. in 25 hits, with Crit Chance and Deadly Strike of +60% each, 10 would be Normal Hits, 6 would be Critical Hits, and 9 would be Deadly Strikes, on average.
if your Crit Chance and Deadly Strike is low, you wont see Deadly Strike very often. with Crit Chance & Deadly Strike of +10% each, out of 100 hits, 9 would be Critical Hits and 1 would be a Deadly Strike, on average.
Brutal Mythic: this Mythic goes on the Chest Item and makes Deadly Strike do Triple Critical DMG!
Imaginary Weapon: 100 DMG.
+50% Crit DMG = 150 DMG.
+400% Crit DMG = 500 DMG.
+400% Crit DMG & Deadly Strike = 1,000 DMG.
+400% Crit DMG & Deadly Strike & Brutal Mythic = 1,500 DMG.
thanks to @Midlumer post that helped a lot.