Hello there.
For this week's Community Engagement Challenge we are asked to share our favorite card combos. I think there are a lot of good ones to choose from, but I would like to share one of my favorite ones I use in Survival. I find it important and beneficial to use effective combos in survival, where there is an added difficulty of cards becoming unusable once they die.
My combo consists of four cards; one Archon, and three monsters. One of the monsters has Weapons Training which explains the number of monsters. I will explain the purpose of each card below.
Archon

For the Archon, I use Possibilus the Wise. In Survival mode where trying to keep as much monsters alive at the end is almost as important as winning the game, the +2 HP to all monsters is very helpful. The Trample adds damage potential to Melee monsters in the team. To further lean in into that strategy, Possibilus also grants Reach to Melee monsters. This opens up more options for team composition.
Monsters

The main monster that deals the damage is Kulu Mastermind. With its Opportunity ability, it takes full advantage of the Trample from Possibilus. Most players put the squishy targets in the middle to the second to the last position, and have a slightly tanky monster at the back to protect against Sneak attacks. This makes Kulu's Opportunity with Trample hit that much harder and more effective.
The second important ability of Kulu is the Weapons Training. It grants 3 Melee damage to monsters with no attack. Usually it will be difficult to position Melee monsters in the backline, but because of Possibilus' Reach, they are not as limited. In the worst case where Kulu gets placed in the first position, it can serve as a tank while the monster behind it can still attack.

The monster I put in front of Kulu is Noa the Just. Noa's Rust is the ability that glues this combo together. Sure Kulu can train other monsters, but without Noa's Rust, the team will take a long time to kill the enemy team if they have armor. Rust makes Trample even deadlier, since it enables Kulu and other monsters to do a double kill. Stats wise, Noa has high Speed and Armor, and becomes tankier with Possibilus' +2 HP.
I usually put Noa in the second position so it can take advantage of the Reach, attack early, and quickly whittle down the front tank. It works well as a secondary tank as long as there isn't heavy magic damage from the opponent.

The monster I put behind Kulu is Merdaali Guardian. Merdaali has the Tank Heal ability which I think synergizes well with Possibilus' +2 HP. So not only can it possibly heal 1 HP higher, but it helps keep most of the tanks alive in Survival mode. If Noa ever dies, having Kulu in front of it can still win battles. Even though it has low HP, it is a cheap heal monster, and I try to put lower HP monsters behind it to protect it against Opportunity attacks.
For the other monster slots, that is where the flexibility of the comp comes in. I usually put any tanky fodder in the first position, and I prioritize HP to take advantage of Merdaali's heal. For the back, I like to add Deeplurker or other opportunity monsters to take advantage of the Trample. I usually put a low HP monster like Hardy Stonefish at the last position as both an Opportunity and Sneak bait/tank.
In a lot of my Survival battles, only the first and last tank dies which are easily replaceable. The core of Noa, Kulu, and Merdaali usually comes out unscathed. There are some cases where Noa will get low, but Merdaali's heal comes in clutch and the team wins before it dies. That is why Deeplurker is one of the top cards I immediately add after the core monsters.
Here are some battles showing the team comp:

https://splinterlands.com/battle/sl_940a09272b8e06fd14a2d0cbbecdbec9?ref=outwars

https://splinterlands.com/battle/sl_1de3e4afa3a8e9110b6713d9f95b374b?ref=outwars

https://splinterlands.com/battle/sl_f1e61d5e8aed690ac431c46be6b5b7e4?ref=outwars
That is it for my favorite combo team. I think it is very effective in Survival mode with how flexible it is. Don't hesitate to let me know what you think, and if you have suggestions for improvement. And as always, these are Not Financial Advice, and Do Your Own Research.
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Splinterlands Referral Link