The Rakuten Eagles introduced a new mascot named Switch earlier today. The mascot was born in California on July 4, 2005. He agreed to a contract worth an estimated 1,776 US dollars. A complete profile (in Japanese) can be found at the link below.
Source: Rakuten announcement 4/1/2016
[UPDATE 4/1 @ 20:43]
A little backstory: The Eagles issued a statement to the media that said they were going to announce the addition of a new foreigner. They made it seem like they were going to introduce a new player, but instead brought in Switch. The press conference, and everything leading up to it, was an April Fools prank, but the addition itself is real.