"You create those like me when you overextend, Sins burned into flesh that cause us to ascend."
This seems to imply that characters with sins become sentient like him. Its his most notable character trait, and we already know that sinned characters can talk to the players at the very least. The important thing about this however, is that it may suggest that Maelstrom is already sinned. It gives a reason why he knows what he knows, and we have an unaccounted for sin. However if this is true, then he now possesses two sins, which may be possible given the original unforgotten realms sins revolved around a single character getting 5 sins, but is unlikely. The other possible sinner is Gwyneth, after she was revived by Galen in GPO, with a spell that specifically says, "Bringing characters back to life may have unexpected consequences," and all of our sins so far, save for Maelstrom's, has involved reviving characters. This is more likely, but it leaves Maelstrom unexplained, although I'm ok with that. This supports the next line,
"And so enjoy your story, the one you picked over me,"
Referring to choosing The Law (Galen), over the Murder Bros (Chimera, possibly related to Maelstrom).
"She will turn on you soon friend, just wait and you see."
Likely referring to Gwyneth, the most important female in the story so far, and one of two sinned females, the other being Lola, a rather minor character. Its mentioned in Lyn's sin donation that "marked Characters will slowly lose themselves to become your servants overtime." If Maelstrom is talking to us here, this probably means that although she will "become a servant" similar to Maelstrom, she will turn on us eventually, somehow.