new set Battle for Zendikar

[LevelX]

I addded the logic to add Zendikar Expeditions lands to the booster.

What would be the best ratio to add the lands? (I set it now to 1 of 20)
In real boosters they appear a bit more often than foil mythics (1 of ~48) correct me if I'm wrong here.

And do the lands replace the basic land in the booster?

[fireshoes]

Foil mythics are approximately 1 in 216 pack, according to this. I'd prefer to keep it a close to the real odds as possible, so it is extra special when you do see one.

Mark Rosewater said on his blog he is 80% certain that the Expedition takes the place of a common in the pack (as foils usually do). Foils are 1:67 cards, according to the ORI booster wrapper (1:4.5 packs), if you want to put in foil logic for booster packs too. I assume they maintain the same rarity ratio as regular packs (10 common:3 uncommon:7/8 rare:1/8 mythic), but that doesn't actually work with the 216 pack number above (would be 540 packs for a foil mythic). It's possible the 216 number is wrong or outdated I suppose.