Hey friend,
I am obsessed with Auto Battlers. I have played Drodo Auto Chess since it was a mod in DotA2, Super Auto Pets since update 3, and TFT since CBT.
I love this game as it feels like SAP, but on steroids as you have to manage 3 lanes.
I have 2 themed decks in mind. Also a potential villain.
Deck 1: Merfolk
Their strategy would center around Shields, but it is different from other decks. Their shields are Bubbles (one time use Shields, I think like the blessing buff? But a dmg redux). The units tend to have low HP, but they make up for that with Bubbles. Bubble buff is stackable, but only in uses. There are also other types of Bubbles, but they all have a Shield as their central gimmick. DMG Bubbles that do 1-3 points of dmg when burst. Heal Bubbles that heal when burst or HoT. Buff Bubbles that increase HP or DMG.
They are caster heavy, but they should have a few tanks and DPS that can make use of the different bubbles. As it is a squishy, glass cannon type deck, the deck would be a hard to use.
Deck 2: Treefolk
This deck is meant to scale decently. Their gimmick is buffs through Buildings. I love the Bank, Smith, and Nurse buildings. In SAP, I love playing Buff teams.
The deck has few actual Units, but a ton of buildings. The whole idea is to take a T1 and grow it into a one-man-army per lane. There can be a Tower Build which shoots arrows, does not move, and does not block. A Healer Build same as Tower but for heals. Etc.
Villain deck: Spectre Queen
This deck revolves around units that move quickly in order to stop any units that have skills that activate "on-step"