I see this example everywhere, that Mystique could gain Sabretooth's powers but not Nightcrawlers, when she shape-shifts. I wonder what other person's powers could she gain.

Along with Wolverine and Sabretooth, she could gain all of the dominant species powers.

Hulk

Icarus

Angel, without the power to heal people with her blood but she can do blood transfusions since she has healing factor although it is probably not as strong as Angel's.

Angel Salvadore, she could probably rearrange her organs to give her acid spit like a fly.

Beak

Emma Frost, without the telepathy but the diamond form

Colossus

Mercury

Dust

Anole

Blob

Toad, without the power to control amphibians

Callisto

Quill

Nope. Mystique doesn't spontaneously gain powers when she shapeshifts. She has a limited amount of healing but she wouldn't gain regeneration if she morphed into Sabretooth, or enhanced senses, or enhanced strength and her claws wouldn't be as strong as his. Hulk again she'd look like the Hulk but wouldn't be nearly as strong or durable as him. Icarus yes she could duplicate wings but not healing factor or mutant voice. She could be as fat as Blob but not invulnerable. She could give herself tentacle arms like Callisto but probably wouldn't have the coordination to use them. She cannot do anything near what Dust, Mercury or Colossus can do.

Oh, well what about Beast, Mr. Fantastic, and the Thing? I remember an episode of the Superhero Squad where she turns into the Black Widow. About Mr. Fantastic, doesn't shape-shifting gives you the power of elasticity? Or is it the other way around? Maybe she could turn into Captain America or the Black Panther. I mean both of them have martial arts skills. Also she imitated Surge perfectly just by appearance but she had a gadget that gave her electricity powers. I can see her being Spiderman without the Spidey sense. She can just use a device to create webs. About Icarus, Mystique can imitate anybody.The reason why I said Dust and Mercury was because in X-Men: Evolution, she turned into a puddle of water. Well, that was after Apocalypse strengthened her powers. So maybe she could turn her body into liquid metal or sand. About Colossus, she can just turn her body into organic steel. She could turn into Luke Cage. All she has to do is turn her skin as hard as bulletproof steel. Maybe she could turn into the Juggernaut.

Actually I think she can now during the back in japan arc her powers have improved and she can duplicate more than appearences and shift organs.

Look, the concept is simple. A shapeshifter can gain another character's powers if those powers are innate parts of their physical form- powers like Mr. Fantastic's, Sabertooth's, or Beast's.

The easiest way to explain it is like this: for the sake of this conversation, we'll separate powers into two groups- 'traits' and 'abilities'. In order to determine whether an individual's power is a trait or an ability, think about how you'd describe the hero's power/s. We'll use Nightcrawler as an example. Nightcrawler is blue, has a tail, is superhumanly agile, has yellow eyes and blue skin, and can teleport.

Three of the attributes I just listed are traits, things that are physically a part of Nightcrawler: Nightcrawler is blue. Abilities are something a person is capable that isn't a physical part of them- Nightcrawler can teleport.