Alexa can roll gaming dice for you: 

“Alexa, roll {number of dice}, {number of sides} die.” 

“Alexa, roll 1, 6 side die.” 
“Alexa, roll 2, 6 side die.” 
“Alexa, roll 3, 6 side die.” 
“Alexa, roll 4, 6 side die.” 
“Alexa, roll 5, 6 side die.” 
“Alexa, roll 6, 6 side die.” 

She can flip coins for you: 

“Alexa, heads or tails.” Or 
“Alexa, flip a coin.” 

She can generate random numbers for you: 
“Alexa, random number between 1 and 10.” 10 scale
“Alexa, random number between 1 and 100.” 100 scale
“Alexa, random number between 1 and 12.” Dice
“Alexa, random number between 1 and 38.” Roulette
“Alexa, random number between 1 and 52.” cards
“Alexa, random number between {lower limit} and {upper limit}.” 
“Alexa, random number between 1 and 78.” Tarot

Want a random fact? 
“Alexa, random fact.” Need to know a factorial? 
“Alexa, what is {number} factorial?”