Each shop slot has a chance of rolling a specific cost of unit depending on your level. This table shows the probability distribution at each level.

Level	1	2	3	4	5
1	100%	-	-	-	-
2	100%	-	-	-	-
3	75%	25%	-	-	-
4	55%	30%	15%	-	-
5	45%	33%	20%	2%	-
6	30%	40%	25%	5%	-
7	16%	30%	43%	10%	1%
8	15%	20%	32%	30%	3%
9	10%	17%	25%	33%	15%
10	5%	10%	20%	40%	25%
11	1%	2%	12%	50%	35%

There are a fixed number of each unit cost in the shared champion pool. This table demonstrates why it is bad to be contested, especially when rolling for 3-stars.

Rarity	Bag Size	Unique Champions	Total in Pool
1	30	14	420
2	25	13	325
3	18	14	252
4	10	14	140
5	9	10	90