Mariano Rivera
ether 5'6 or 5'4
Tommy Bond
Sure, but it is usually with the approval of the team's manager.
His team has to record 27 outs while he was the pitcher of record.
In MLB, it is a balk.
The MLB pitcher that was nicknamed the "Rocket" was Roger Clemens.
In MLB for the 2009 season, that is Jamie Moyer of the Philadelphia Phillies at age 46 (born November 18, 1962).
The heaviest pitcher in MLB History is definitely Nolan Ryan.
There is nothing I have found in the MLB rules that would prohibit a pitcher from a pitching motion similar to that of a softball pitcher. Actually, the underhanded motion was the rule when Alexander Cartwright came up with the rules of baseball in 1845. I have included a link, named 'MLB Rule 8', to the MLB rules concerning the pitcher on this page.
MLB rule 1.07 defines the dimensions of the pitcher's plate as 24 inches by 6 inches. There is no dimension given for its thickness, or depth.
The pitcher was Bob Gibson. MLB lowered the mound in 1969. In 1968, Gibson went 22-9 with a 1.12 ERA and 268 strike outs.