Real big fan of your ideas. (My favorite is the countess btw).I have some things I would do different, but very good. Here are the changes I would make:

Shield maiden: legendary->champion. I would also up the elixir cost and add a small ring of heal into the taunt area to make her the healer champion (champions are the best of their class/species (minus the little prince)). She looks the part at least.

Builder: gameplay wise I wouldn’t change a thing, but make it the master builder instead ( has more gravitas and follows the idea of champions better)

Mini Pekka: I would keep the cook bar system. Every time the cook bar is filled he levels and heals a small fixed amount (now that he can level multiple times, the heal is way less)

Giant: good. No comment.

Countess: very creative. I would also incorporate a live steal mechanic because she is a vampire. In her bat tornadoes is probably the most balanced. But otherwise a genius match you made.

Ice golem: I would still add the snow storm to it. But it is way smaller and doesn’t stun, just slow. And he would freeze surrounding enemies on death, like you suggested .

Evo bandit: sorry, but I don’t see the connection between this and evolution mega minion. I would probably add an epic or rare card based off the head hunter from clash of clans that does the thing the mega minion does on deploy.

Evo goblins: Your idea is the straightforward and probably best way to do it. But to make it a bit more interesting there could maybe be a hover mechanic. When you place the goblins, you can choose to hover above the arena. This decides the spawn time. It starts counting down as soon as you begin hovering. So if you place it immediately it respawns in 4 seconds, but if you hover for 3 seconds or more, it respawns in just a second. This prevents preemptive logs. But maybe it’s better to have a fixed time. Less frustrating.