Amulets first.
To be possible, you need to be clvl 86. But it becomes more an more likely up to clvl 95 (it is a gamble, after all). You need the item level to come out as at least 90, but the item level is random between your level -5 and +4, so the higher you are, the more of that random range will be over 90. At 86, only 1/10 of your gambles will be level 90, and that is before it even rolls the mods.
Crafting is more complicated. That depends on both your level and the item level of the main ingredient (ie the amulet in this case). The output item level wil not be random, it will be [clvl/2] + [ilvl/2] with both rounding down. Again, that has to be at least 90 to get +2 skills. So if you are clvl 90 you have to use amulets that are at least 90, but if you are clvl 92 you can use amulets that are only 88, etc.
The ideal level is 93, because then you can gamble an amulet, which will have level at least 88, and then when you craft you know it will be at least 90. At 92, you could be unlucky and gamble an 87, and that would only come out as 89 after the craft.
Has anyone noticed how many numbers I put in my posts here?
Now, circlets. These are different because they get a bonus to their alvl. Plain Circlets (ie not coronets, tiaras, diadems) get +3. So to hit the magic 90 they only need to be at least level 87. Which means you could gamble one as early as 83, but your chance improves up to clvl 92.
Coronets get +8, so you could gamble one as early as 78, but your chance improves up to clvl 87.
There is a further chance when you gamble a coronet that it will upgrade to tiara or diadem. These can spawn +2 skills at even lower levels (in fact diadems can always spawn +2 skills at any level). However, you can't ever know you will get the upgrade until you try, so it isn't an efficient way to fish for them. Also, you can't gamble a Diadem until you are getting ilvl 85 items anyway, by which time your coronets can get +2 skills themselves.
Or you are remembering back to a little time ago. In 1.09, lots of monsters (everything from A3 Hell) were mlvl 90.
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