Mythical items are hard to get with the new campaign its a little easy but too hard for someone so my opinion is that there should be a mythical item box with stats like this:
Mythical items 1%
Legendary items 5%
Epic items 10%
Rare items 20%
Nothing 64%
Cost 10,000 SMs

Agreed, this has been suggested time and time again, I believe Ogonna suggested it first. Hopefully they'll implement this one day, but chances are they won't, because it'll bring down their revenue with people wanting to take chances with the 1% instead of wasting real money on a 5% chance.