Consecrate is a 2nd-level spell and disintegrate is a 6th-level spell, which is totally bonkers as far as I can tell. Undead tend to be the more common threat in most campaigns, making the truedeath crystal more valuable, not less. Of course, their costs reflect that, with truedeath being substantially more expensive (at the lesser and greater tiers), but it’...
We can't tell you what sort of rulings your DM should issue. This is especially complicated because the two crystals you cite seem to have very different costs: the greater truedeath crystal costs 10000gp (5000gp more than the lesser truedeath crystal), but the greater demolition crystal costs 6000gp (3000gp more than the lesser demolition crystal), even ...
From the Player's Basic Rules:
When you score a critical hit, you get to roll extra dice
for the attack’s damage against the target. Roll all of the
attack’s damage dice twice and add them together. Then
add any relevant modifiers as normal. To speed up play,
you can roll all the damage dice at once.
For example, if you ...
It depends whose turn it is, if you are using Xanathar's Guide to Everything
Adamantine armor provides an ability that triggers off of critical hits. Rather than preventing them from occurring, when one happens it is converted into a normal hit. Similarly, when the hit happens the attacker might have abilities like your example of Great Weapon Master ...
If it's not a critical hit, then it's not a critical hit. The adamantine armor specifically states:
While you're wearing it, any critical hit against you becomes a normal hit.
A hit remains functionally different than a critical hit. If the mechanic turns a critical hit into a normal hit, then anything that keys off it being a critical hit won't ...
AKA: the very worst kind of answer.
From your comments I think what you are really asking is "If a critical hit on adamantine armor would have missed except for being a crit, does it still hit?" If I am wrong on reading your question let me know. But assuming I am not, then the answer is the same for any other attack roll that you make. You hit ...
The attack hits, but becomes a normal hit.
At the point where the effect of adamantine armor comes into play, the wearer has already been hit. Features and effects do what they say they do, and adamantine armor does not provide a way to convert a hit into a miss.
Improved Critical hits on a roll of 19.
The feature states that attack rolls of 19 hit.