Wargroove

The games 200 stars are split up like so

Arcade Mode - 75 stars
Story Mode - 99 stars
Puzzle Mode - 25 stars

The final star is hidden and requires unlocking a secret character (also needed for 5 of the stars in arcade mode).

To unlock the hidden character first you need to have at least 151 stars across the various game modes and you need to have finished the story including the Epilogue. Once you have those you need to do each of Caesar's side missions again where you can find a statue located on each map. You need to play these maps IN ORDER and have Caesar stand on top of the tile with the statue and Wait. Once you have triggered the statue and received an orb you MUST win the map.

To make this process easier you can adjust your difficulty settings so that you take very little damage and receive 500 gold per village instead of the standard 100, this should make clearing levels much simpler.

The location of each statue is as follows

Act 2 - Side 1

https://imgur.com/a/NZJd6wX

Act 3 - Side 1

https://imgur.com/a/tFtNxar

Act 5 - Side 1

https://imgur.com/a/DEzbtJ5

Act 6 - Side 1

https://imgur.com/a/Q1zH2Uz

Once you've located each statue and completed the final Act 6 - Side 1 you will get small scene and unlock the secret character Mercival.

With Mercival unlocked you need to run through Arcade Mode with him on hard to get those five stars, you can then begin working on your 200th.

To unlock the final star you need to use Mercival's Groove called Gone Fishing which sees him cast a fishing rod into an adjacent body of water and catch a fish. You need to catch one of every fish in the game and once that is done you will get your star.

Fish

Boots: Common, appears in all water tiles
Piano Tuna: Common, appears in all water tiles
Gingery Guppy: Common, appears in all water tiles
Jerkfish: Common, appears in all water tiles
Salty Bass: Common, appears in sea only
Pinchmaster: Common, appears in beach only
Fruitfrog: Common, appears in river only
Lemon Loach: Uncommon, appears in all water tiles, Grass biome only
Strom Jelly: Uncommon, appears in all water tiles under rain, Grass biome only
Lime Sole: Rare, appears in all water tiles, Grass biome only
Eclectic Eel: Uncommon, appears in all water tiles, Ice biome only
Dreadfish: Uncommon, appears in all water tiles under snow, Ice biome only
Snuffish: Rare, appears in all water tiles, Ice biome only
Toy Koi: Uncommon, appears in all water tiles, Desert biome only
Clockwork Fish: Uncommon, appears in all water tiles under sandstorm, Desert biome only
Red flapper: Rare, appears in all water tiles, Desert biome only
Chucklefish: Rare, appears in all water tiles under severe weather condition
Starfish: Common, but must have caught all other 17 fishes, and must have 199 stars

To make this process easier there are premade maps by Steam user Kitsune which allow you to fish as much as needed without interruption from the AI.

To use these maps first go to the custom maps menu and press then enter the following codes

Grass Biome - XVA7DF2Y
Desert Biome - TX6V4S8S
Ice Biome - 347Y5DM9

To play the maps go to Multiplayer, Local Game then go to the last of the map tabs and scroll to the bottom to choose your biome. Once in the game simply fish until you at least catch all three of the biome specific fish then move on to the next one as you should catch all the universal fish as you work towards the others.

Once you have the first 17 fish and 199 stars you can catch the Starfish. Once done finish the level to collect your 200th star.

Credit to Steam user horheristo for the statue location maps.

This isn't an in-depth solution so much as some advice i've gathered trying to beat the arcade missions on Hard.

I've found cheesing to be the way forward, as in rushing the stronghold or captain to try to beat them down after stalling the bulk of the army. Try to lure them over to one side and store up a couple high power units before dashing for the base. I think they focus on where the number of units are, not the strength.

I've found massing weak 100g soldiers on one side or mermen, and a few dragons or colossus on the other means they'll ignore the dragons and you get a shot at the base.

Alternatively, you can attempt to bait with your hero, this works better with some than others. for example i managed to bait my way through with Ragna and her Groove, using it to jump over impassable terrain and getting the enemy hero into a position to be hit by trebuchets or dragons etc.

With the arcade though if you lose 1 out of 5 you will have to restart so making it through 15 runs on hard means 75 wins in streaks of 5. Will update as more info is known.