>>532812083
SSS tier: anniversary 6* selector + 10 pulls for $30
S tier: monthly pass, weekly gold collection, 2 pulls for $2 packs
A tier: offer of the month, 4 pulls for $5 packs
B tier: double crystal drops (resets every anniversary)
C tier: everything else

If you buy the more expensive packs, you're actually paying for the other materials rather than the pulls