It's pretty good, but I don't think it truly captures the spirit of the character; the intimidating, chosen warrior. He looks more like a member of the royalty than a soldier.
But I really like the contrast with your other piece, The Hollow Knight.
Edit:
For the transition animation, you could probably use any program which allows you to edit GIFs, for example Photoshop, After Effects; or ScreenToGif, probably GIMP…
Look for "crossfade animation".
This is a relatively simple trick, so you might even use an online editor like this one: https://ezgif.com/maker
Upload the two images, increase the time delay and make sure you tick "Effects / crossfade frames" and it should do what you want.
https://ezgif.com/help/how-to-create-gif-slideshow