How to win with this deck:

Step 1 - Hard-mulligan for Symbiote Suit and play it ASAP. Fertile Ground and Deft Focus are also top-priority targets.

Step 2 - Flip every turn to build up growth counters, and play as many upgrades as possible in your early turns, prioritizing the four Groot hero upgrades: Entangling Vines, Lashing Vines, Vine Shield, and Vine Spikes. Second priority after those would be Unflappable, Armored Vest, and Hard to Ignore, in that order. The 3 retaliate upgrades are last priority, probably post-shuffle material, unless you're facing Tough enemies or Ultron bots.

Step 3 - Use those 9 defense events to protect your growth counters. Your goal is to stay near the full 10, spending 1-3 counters on your card abilities each hero turn, and flipping down to alter-ego when you need a refill. By the midgame, you should hopefully be able to stay in hero form 2 turns for every flip down to alter-ego, and fully block some attacks for your teammates. Manage threat with Hard to Ignore and "I am Groot", while murdering minions with Root Stomp, Vine Spikes, and your buddy Rocket. Use your untap abilities after blocking, if possible. Only use Lashing Vines for ATK or THW if it gets a bad card off the table.

Step 4 - Close out the game with your thinned-out deck full of discounted superhero events. Or let your teammate(s) finish off the villain. What have they been doing all this time, anyway? Besides dealing with all the extra encounter cards that came with your Symbiote Suit :)

Update 4/24/2023

-2 Indomitable (one left in the deck for emergencies)

-1 Flora and Fauna

+3 Multiple Man

Never got to Flora/Fauna once in ~5 games of testing, so it's out.

Turns out Multiple Man is an all-star card in this deck. Hitting the table and immediately thwarting for 3 can save the game, not to mention pinging off Tough status, and chump-blocking for days. We are thinning the deck, allowing for more Upgrade draws, while protecting the board. Make sure to kill them all off before you shuffle! Oh, and playing We Are Groot the turn after dropping MM feels amazing. Chump blocks for DAYS. This update got me my first solo win, versus Rhino+Armadillo, who I have dubbed The Tough Boyz.

I've also realized that playing Symbiote Suit on turn 1 may be great in multiplayer, but it is god-awful in solo. Discard that thing for a resource, until you've got your board set up and shuffled at least once! I would still recommend this deck primarily for multiplayer, but I think all the True-Solo Kings/Queens out there can still have some fun against scenarios that aren't Mutagen/Ultron/etc.