Trials of Gnomus update added two new characters for the plant and zombie sides: for the zombie side, we got Hower Goat-3000, and for the plant side, Torchwood. However, unlike other base characters, you need to do specific quests, and they do not appear on any kind of sticker pack. Both of them have different stats and weapons. If you want to know about their abilities, take a look at the wiki:
https://plantsvszombies.fandom.com/wiki/Hover_Goat-3000
https://plantsvszombies.fandom.com/wiki/Torchwood_(PvZ:_GW2)

Anyway, the first step is to get 4 different recall key cards, and for that, you need to open the red chest that only appears in Town Hall, which costs 50 Rainbow Stars. Town Hall only opens at the start of the month for 10 days, and after 10 days it closes. When Town Hall opens again, the chest will be openable once again. You can get rainbow stars by playing Town Hall game mode or by making a deal with a seagull on Town Hall. You can trade 7 stars for 1 rainbow star, but I recommend playing the Town Hall game. Red chest only gives you 1 key, and you need to wait for another Town Hall event (Town Hall to reopen) to once again open red chest for 50 rainbow stars to get other keys. Only Red Chest gives you keys for opening new characters. Basically, you need to wait 1 month to get one key.

The second step is to go to Town Hall and trade 25 stars for a key. After you take the key, you need to go down the sewers. You will see a locked door. You will open the door and go inside.

The third step is where you use recall keys for starting Trials of Gnomes. Inside the portal, there are 4 doors: red door needs red key, blue door needs blue key, etc.




And inside the portal, there are quests where you need to go to the other side. These quests include:

Trial of Shooty-Shooty

The player must shoot all the copies of the image shown on the doorway. In the beginning, there is only one image required; however, more and more copies of the required image will start to appear in later rounds.

The player is given 53 seconds to complete the trial.

Trial of Recollection

The player must shoot all the copies of the image shown on the doorway. In the beginning, there is only one image required; however, more and more copies of the required image will start to appear in later rounds.

The player is given 53 seconds to complete the trial.

Trial of Balance

The player has to cross many different platforms, including small circular platforms and long, winding platforms suspended over a lava pit. Along the way, there are projectiles and giant hammers that can vanquish the player.

Being vanquished by either falling into the pit or getting hit by a projectile or hammer will result in the immediate failure of the entire trial.

Trial of Hot Doom

The goal is to get to the finish, passing four different sections of platforms. These platforms will light up in orange and red. Landing on an orange platform will result in a vanquish.

Getting vanquished, either by the platform or falling through the gaps, will result in the failure of the entire trial. The player has 1 minute and 8 seconds to complete the trial.

IMPORTANT: On each trail door, you will see random symbols. You need to screenshot these codes. After you screenshot these codes, you need to go down to the portal where you stepped on the code you screenshotted. After this, you will fight a boss fight. When you beat the boss, a portal will open next to the gnome statue. You need to go inside this portal and take a screenshot. Inside the portal, you will see two empty blocks. Those two empty blocks, for example, 5 and 8, are empty. You need to look for the first code you open the portal with, and let's say 5 is a plany pod and 8 is a shoe. You need to write it down for the last step.

The fourth step is using the code you wrote down. You can find what I mean in the IMPORTANT part. After that, you need to beat Rainbow Boss. After you beat him, the Gnome Statue will break

Last Step Inside the Gnome Statue there are two chests: one for plants and one for zombies. Two of the chests have five locks. Each lock needs 15 rainbow stars.

It's good to know that after you destory the Gnome Statue Rainbow Stars Pack, it will be available and give you 30 rainbow stars for 225,000 coins, so you don't have to play the Town Hall game or use Normal Star to get a rainbow star. After you unlock the two characters, the sticker pack will disappear.
The plant chest includes torchwood. And Zombie Chest includes Hover Goat 3000, after you open both of them that's it. You unlock the characters.

Please rate and tell me if anything in this tutorial does not work.
Have fun with secret characters!