So the idea for this sprite is that it restricts the movement of enemies.

First skill/appearance:
looks like a small, finless shark. (Still has a tail) White and grey are the main colors
Icy punch: Slams enemies back, then freezes them. It's a melee attack that only affects one enemy and those behind it. (you might get two or three with minis) Only the first monster takes direct damage.
Upgrades are cooldown time, distance slammed, severity of freeze
Icy punch upgrades into:
Permafrost punch: a mist hangs around the impact site for a bit. Icefish gets a fin under its chin
Avalanche punch: slams more enemies back. Icefish gets more noticable teeth

Second skill/appearance:
Slightly bigger. Has side fins. Dark grey elements added
Frostfield: creates four blocks of ice around you. They will shove away enemies and last for about 3 seconds initially. No freezing, but they block monster ranged attacks. They also protect you from melee attacks by preventing monsters from getting close to you (won't work for lumbers.) You and your fellow knights can move and shoot through the blocks, though.
upgrades are cooldown time, duration of ice, size of blocks
Frostfield upgrades into:
Frozen sea: more ice blocks pop up further away. Icefish gets a set of horizontal fins on the tail
Frostarmor: Ice blocks provide a defense boost to any knights nearby them. Icefish gets a pair of black patches on its head by its eyes

Third skill/appearance:
Larger. Has more dark grey elements added. Head is slightly defined from the body.
Cryowave: A massive shockwave that slams enemies away and freezes them. This shockwave originates from about two squares in front of you, so it will slam enemies close to you into you.
upgrades are cooldown time, size of the shockwave, and freeze power
Cryowave upgrades to:
Cryofire: Icefish creates an effect that looks like a hurricane and constantly refreezes enemies - with damage - for the next few seconds. Icefish gets a dorsal fin - two or three of them in a ridge.
Cryoskate: Allies get an MSI/ASI for a few seconds, while monsters that move may just randomly get knocked down. Icefish gets a dorsal fin and a larger tail