1) We've discussed an infinite play mode that gets unlocked after winning, that does down underground and gets progressively harder. A sandbox mode is a cool idea too!
2) There is currently a debuff in-game already (Rocky stuns attackers), but it's not communicated very well visually yet. I'll be adding more for sure, maybe even from special items and not necessarily the minions themselves.
3) Great suggestion, I plan to add a mouseover on the minions like the defenders so you can visualize their ability range. I could also add it to the cards.
4) Upgrades will definitely happen. Right now I'm thinking they'll be finite and potentially share a system with equipment slots.
5) We'll definitely be adding either selling minions, combining them into upgraded versions, or breaking them down for parts (gruesome, I know).
6) Really cool idea! Maybe a relic could summon a very powerful minion after certain conditions that's not directly purchasable!
Thanks again!