On the second screenshot, there's clash between SMB3 BGOs and SMW Grass Tiles. I remember reading something about that in the Community GFX Pack.
Yeah, there is, but it says that is Ok if used correctly.
Even more, clashing has nothing to do with versions. If you find something that is from SMB3, other that is from SMW, combine them doesn't means it's bad. In fact, if it's a fine combination, it evens gets a bonus score for clever use of more than one style.
There he used SMB3 bgos and SMW tiles, but if you ignore the facts that is SMW and SMB3, and you're seeing this for the first time, you can tell it's okay.
It's a WIP, right? It's a good beginning, I guess. Boss rushes aren't very appreciated here, but who knows you can show us a exception?
Try to make creative use of power-ups, blocks and tiles in battle, look forward custom graphics to try create new bosses no available in the default NPC list, and learn how to use layers and events. If you do those thing, you'll be walking in the road for a good episode.