Originally Posted by JSensei

I wonder what the actual mechanism is. All three that I described essentially yield the same result, just via three different paths. The third one sound the easiest to code though. X points = tier.

Throw in another random number generator to get the wait time for that tier.

Then use a third RNG for the item(s) that you get. Every combination of items available for a certain point value just need a discrete value or range of values. Spin the RNG and get whatever it lands on. Seems pretty simple to me.

It is:

For R1(reward tier) =I1(item)+I2+i3+i4
For R1 set T(time)(rng =100%,=200%,=300%)
Count T
Present R2 (rng x1I, x2I x3I, (rng itemset)

Not much different then that...Of course you set ranges on the rng and such but once coded the snippets can be recycled as needed.
Its how they code the gatchas and reward boxes... code once then just plug in the appropriate values for the variables.