4 Color Istanu
Istanu is a super powerful card in a lot of matchups when used properly. The swallow mechanic as a whole has lost popularity, leaving Frogify as the only real threat to Istanu. When paired with lots of sturdy and efficient collectors, Istanu's recurrence is very hard to deal with as you have to clear the entire board to prevent the effect. Cards like Sturdy Shell and Ancient Boar can take a hit and function well in the early game (when multicolor decks tend to struggle). Blue + Red is imo the best combination for primary colors as:
1. Best green cards for the deck require 1 forest
2. Can't run any other yellow as want to get Istanu from Ulani everytime
3. Red is the best at clearing little dudes (good most of my high stated dudes)
The Ancient synergy cards in general are very strong vs midrange and aggro and give us a better matchup vs stuff like yellow tempo (still unfavored) and RG crackthorn (favored). The hardest matchups are Dreamreaver and Blue jump, probably. Proper placement of lands and the Ancient Boars makes rush matchups pretty even. For other slow decks (like Gemshell), Istanu will pretty much win the game on its own, just make sure to play around double aoe as that is often the only way they can clear Istanu and win (like getting Istanu to 3 health and having other creatures or having a 3/7 Shifting Octopus).
Land placement it a little challenging at first. 4 color decks always have complex set up early, and this deck also has to keep in mind Ancient Boar paths and Istanu setups. In total, you want 3L/2M/2D/1F. Setting up the mountains is fairly arbitrary since the only creature you have to think about is Garudan. The forest is often the hardest spot to pick as you really don't want to drop another forest early for Boar. The deserts are preferable at the wells or dead center of the map. Really though, that only matters for the initial Istanu drop (and if you have Failed Experiment then doesn't really matter).
The only change I'm considering currently is possibly:
1 Ancient Herald => 1 Curious Biomancer
If you have any ideas, I'm all ears.