Thanks for the great feedback on sprite design, with more time I think further improving the sprites and adding animation would be a high priority.
About poison towers, I think the card was a bit unclear too; they are support towers who grant poison abilities to all attacking towers within range. So they're powerful, but only next to other towers. Although maybe damage over time isn't that important when bombers and snipers can OHKO in a lot of cases... Definitely more balancing needed here too, 48 hours is so short!