He made his Major League debut last year and went 3-6 with a 7.88 ERA (42 earned runs/48 innings) in 14 games, nine starts for the Mets. Flexen was the Mets 14th-round selection in the 2012 MLB Draft.
Nido, 24, began the year at Double-A Binghamton of the Eastern League and hit .278 (5-18) with five RBIs in five games for the Rumble Ponies. He was recalled on April 11 and was with the team until he was optioned to Las Vegas on May 9.
He hit .135 (5-37) with one double and one RBI in 17 games for the Mets this year. Nido batted .300 (3-10) in five games with the Mets in 2017.
Baumann, 30, is 0-1 with a 19.29 ERA (five earned runs/2 1/3 innings) in two games this year with San Diego and New York. He was claimed off waivers by New York from San Diego on April 27.
Lobaton, 33, hit .152 (7-46) with two doubles and three RBIs in 18 games for the Mets this year.