Since Atomiswave emulation isn't as versatile as Neo Geo emulation as of this writing, exploring the graphics data isn't as easy as it once. Best results seem to be from loading digging through the VRAM in save states of the PlayStation 2 port or Metal Slug Anthology on PSP.
This game has new characters, so you know what that means: needlessly converted animations!! Ralf and Clark get their own versions of unused animations from the previous games, seemingly using Metal Slug 5 as a basis on what animations were carried across. The throwing animation with the dual machine gun still cuts off like it did in that game, for instance.
Not all animations were converted for both characters; only Ralf gets to try out the aiming-backwards animations from MS1, while Clark hogs some aiming-upwards frames to himself. Credit goes to RandomRebelSoldier for ripping Clark's sprites.