Part 1
The first thing that we all read is a grammar mistake, proofread the entire comic before uploading it, and try to use varying sprites of mario, to add expression, when he and luigi are confronted by the boo's, it is a standard stand-still sprite, that doesn't really add to the "OMYGODBOOS" expression.
Part 2
Grammar mistakes are easy to spot, again. "Are they no more alive?"(P.1) should be "Are they no longer alive?" "How do you mean, no?"(P.2) should be "What do you mean, no?" and after "well actually"(P.3) there should be a comma, not a period. In Panel 4, Luigi should say something like, "I wish I had never had a brother throughout my entire life," there is no need for "In this time" and the spelling mistake of "eternal" of "entire" is evident.
Expressions were improved on in this one though. Examples being Boo closing his eyes at the bad news, and Luigi's expression in panel 4.
Part 3
I liked this one, because you captured what Wario is like really well. And the expression he gives at the diamond is really well suited. In fact, all of the expressions are, on both characters, Kudos on that.
Grammar mistakes are dropping in amount, but still visible.
Part 4 (NEW)
Only thing I can say abou this one is that it isn't "Hero's" (At the top left of P.1) but "heroes."
Part 5 (NEW)
Work on captialising "I's" and also adding questionmarks in where needed. (Example: When mario says "Where am I." instead of "Where am I?")
Otherwise, it's reasonable. It's not as funny as it could be, but the story is easy enough to follow, and I think it has reasonable prospects. Make sure you read over everything and correct all grammar mistakes. You could even type up all the dialogue in word before adding it to the comic if you are unsure, so that it will be nigh on, if not, perfect.
-Josh