Suddenly is an adverb and its comparative is formed by putting the word "more" in front of it.
It is most suddenly and most suddenly
more suddenly, most suddenly
"Suddenly" doesn't have a comparative and superlative form. Instead, you would say "more suddenly" or "most suddenly."
The comparative form of many is more
"Truer" is the comparative form of true.
The comparative form of handsome is handsomer
The comparative form of solid is solider
The comparative form is: more central.
The comparative form of good is better.
The comparative form of full is fuller
The comparative form of sunny is sunnier.
Safer is the comparative form of safe.
The comparative form of friendly is friendlier.
The comparative form of dreamy is dreamier