Hi Stella,
There are two things that combine to provide an answer to that question:
- Different types of chests contain different rarities of troops. For example, Gold chests contain common and rare troops, Glory chests contain rare troops and above, Gem chests contain Ultra-rare troops and above (with higher probabilities of getting epic, legendary and mythic troops than Glory chests). I’ll come back to guild chests and event chests below.
- Newly released troops don’t go into the drop pool for the relevant chests until 4 weeks after release. For a list of what is NOT yet available, see here:
Event chests have contents that vary based on the current week’s kingdom. They are like gem chests, except that they only have epic and legendary troops from the weekly event kingdom (Mist of Scales for this week on PC/Mobile), and mostly kingdom troops for the ultra-rares, although you will sometimes get some random ultra-rares from other kingdoms.
Guild chests vary based on how many seals your guild has earned for the week. For every guild chest that you open, you first get a 50% chance of getting a Guardian troop, then a troop (or traitstone) from the relevant rarity levels. For example, if your guild has not earned any seals yet, the chests only contain common and rare troops (like a gold chest) for non-guardian troops. The more seals your guild earns, the better the troops that are available from guild chests.
I hope that is a helpful reply - if you have further questions, just ask and someone will answer!