Docs

Know Your Classic and Magic Cards

This article covers only cards used for Skylanders (Mifare S50 1K).

Type 0: GEN1 UID Locked Cards: *

63 blocks (excluding Block 0) can be re-written multiple times if you have the custom keys for this UID.
UID cannot be changed. 
Answers to Chinese magic backdoor commands: NO 

Protocol	UID Length	Size	Mechanism	Android NFC	ACR122U
Mifare S50	4 Byte	1kb 16 sectors 64 blocks	Use SkyUID	Can’t change UID (locked)	Can’t change UID (locked)

Advantages of Gen1 Classic Cards:

More global support software wise.

Disadvantages of Gen1 Classic Cards:

UID cannot be changed.
If wrong data is written, card is dead permanently.

Those are the official Mifare Classic S50 1K 4 Byte access cards.
They are NOT Magic Cards.

Type 1: GEN1 A UID Changeable Cards: *

All blocks (including Block 0) can be re-written multiple times 
Uses "backdoor" technique to change/rewrite UID. 
UID can be changed multiple times. 
Answers to Chinese magic backdoor commands (GEN 1a): YES 

Protocol	UID Length	Size	Mechanism	Android NFC	ACR122U
Mifare S50	4 Byte	1kb 16 sectors 64 blocks	Backdoor Command	Don’t Support UID Changing	Support UID changing

Advantages of Gen1a Magic Cards:

Super fast to change the UID
Recoverable after invalid data written
Cost-effective for Mifare S50 cloning

Disadvantages of Gen1a Magic Cards:

Some access systems may not allow this magic card to pass because of it can be identified with its built-in controller.

UID Changeable cards are used to duplicate Mifare Classic S50 1K 4 Byte access cards.
Those are also know as Chinese Magic Cards.
Generation 1a tags are unlockable with code 0x43 0x40.
There is also Generation 1b tags that are generation 1a tags with custom unlock code.

Type 2: GEN2 CUID Cards: *

All blocks (including Block 0) can be re-written multiple times 
Not easily detectable by a system with "anti-clone" feature 
IMPORTANT: Card will die if an invalid Block 0 is written 
Answers to Chinese magic backdoor commands: NO 

Protocol	UID Length	Size	Mechanism	Android NFC	ACR122U
Mifare S50	4 Byte	1kb 16 sectors 64 blocks	Keys authentication	Support UID Changing	Support UID changing

Advantages of Gen2 Magic Cards:

Easy to change UID on the Android Phone.
Cover most access systems, no backdoor.

Disadvantages of Gen2 Magic Cards:

Cause dead sector if written with invalid access control byte.
Unfixable if written with invalid block 0.

There is also a Gen2 OTW FUID type which is “One-Time Write UID” (Once written, UID cannot be changed). Avoid those.
Also not all Gen 2 CUID tags are exactly the same either, because it depends who manufactures them.
Most Gen2 CUID tags will have SAK: 08 and ATQA: 0F01. Those will be recognized as “NXP Mifare Classic (MF1S50)”.
Some Gen2 CUID tags will have SAK: 08 and ATQA: 0004. Those will be recognized as “Unknown Mifare Classic IC, possibly cloned”.
However others Gen2 CUID tags have SAK: 81 and ATQA: 0004. Those will be recognized as “Unknown IC” or “Not a MIFARE Classic tag!” and might not work for Skylanders.
Read more about it here: Mifare Classic - SAK Swapping Explained
And more about the different SAK and ATQA types here: ISO/IEC 14443 Type A

Type 3: GEN3 Cards *

Protocol	UID Length	Size	Mechanism	Android NFC	ACR122U
Mifare S50	4 Byte / 7 Byte	1kb 16 sectors 64 blocks	Backdoor Command	Don’t Support UID Changing	Support UID changing

Advantages of Gen3 Magic Cards:

More protocols support
New Mechanism to change the UID
UID can be locked permanently

Disadvantages of Gen3 Magic Cards:

Locked UID cannot be unlocked

Those use another type of backdoor command compared to Gen1.

Type 4: Ultimate Magic Gen 4 *

Advantages of Gen4 Magic Cards:

Use latest technology, have a lot of extra features.

Disadvantages of Gen4 Magic Cards:

Expensive

The Ultimate Magic Card is multi-purpose emulation card, supporting customisable card type, card configuration and functionality mode. It is essentially a completely configurable emulation platform in card format. Those are also expensive.

Sources:

http://www.proxmark.org/forum/viewtopic.php?id=6545

https://lab401.com/products/ultimate-magic-card-gen4

https://lab401.com/blogs/academy/know-your-magic-cards

https://shop.mtoolstec.com/product/uid-changeable-1k-s50-chinese-magic-card

https://shop.mtoolstec.com/whats-the-difference-between-3-generations-of-mifare-magic-card.html

https://www.everythingid.com.au/rfid-access-cards-c-3/uid-changeable-m1-s50-block-0-writable-cuid-fuid-gen1-gen2-card-p-8