Plarail has released two sets that include an exclusive twin:

⚫The Donald and Douglas snow plough set : https://thomasmotorized.fandom.com/wiki/Donald_and_Douglas_Snowplow_Train_Set (1999)
⚫The Bill and Ben harbor friends set : https://thomasmotorized.fandom.com/wiki/Bill_and_Ben_Harbor_Friends_Set (2004)

The Donald and Douglas snow plough set:

In the The Donald and Douglas snow plough set the exclusive twin is Douglas. Eight years later he was released in the UK in the MR&R range with a few differences:

The plarail one had the old tomy logo and copyrighted 1998 (Not 1999 as the sets were probably made 1 year before release ). He also has his eyes facing downwards. He also came with an unique and exclusive snow plough sloped down towards the right.

MR&R Douglas

Plarail Douglas on the right

MR&R underframe

Plarail underframe

2.The Bill and Ben harbor friends set

In The Bill and Ben harbor friends set the exclusive twin is Bill. Five years later he was released in the MR&R range with a few differences: 

The Plarail model had the eyes facing towards the right and only had ©Britt Allcroft(Thomas) Limited 1999 and nothing else.

Plarail Bill and Ben

Markings

Plarail Bill, Ben and MR&R Ben

Personally I own a MR&R Donald and Douglas, a Plarail Bill and Ben And a MR&R Ben