Loop Hero can be insanely hard if you play relying solely on the game's RNG or if you mindlessly throw tiles in the darkness without thinking ahead. It took me a lot of tries to defeat the Lich, but after I realized there were tile combos that could boost my status and give me a huge advantage, the game went from insanely hard to just hard.
A quick tip on how I found most of those combos. Before placing a card, drag it around close to other tiles. If it changes appearance, it's because the card will receive a different effect when placed. If you are not a fan of trial and error, here are eight tile combinations and their effects.
If you place two Battlefields cards close together so their blue area of effect overlaps, Blood Clot enemies will start to spawn every 4 days. They are one of the weakest enemies, so they contribute to your loot hoarding in every loop. Also, two more chests spawn due to the Battlefields is a great bonus for Warrior and Necromancer. Unless they start to bite you.
After unlocking the Village Card, you can place it next to a Vampire mansion, or vice-versa, so it becomes a Ransacked Village. At first, you will lose the Village's healing effect and 4 ghouls will spawn at each loop. But after 3 loops, it will turn in the Count's Land, which has better healing than a village and gives you quests with better rewards.
When you upgrade the Gymnasium you unlock the Suburbs card. Placing five of them in a cross-shape will create a Town and increase the experience gained from killing enemies by 2. You can create how many Towns you want, and fortunately, they don't have any downside. So rack up your exp to pick up a multitude of traits.
In many loops, you will be unlucky enough to get bad equipment or cards, indicating that a gathering run is your best option. The best card at these times is the Treasury, which provides you with a random resource after placing anything on an adjacent tile. If you fill up all the 8 tiles around the Treasury, it becomes an Empty Treasury and gives you a lot of bonus resources. But as every action has a consequence, gargoyles will start to spawn every 3 days. But so far, gargoyles weren't a big threat for my hero.
A must-have combo for any Warrior run. By placing 9 rocks or mountains in a three-by-three square formation, you will get a Mountain Peak. It grants you +120 HP and +5 additional HP for every adjacent mountain/rock tile. On the downside, it will spawn a harpy every 2 days. Important to note: if you place 10 rocks or mountains, a Goblin Camp will appear which spawns hard-fast-hitting Goblins every day. Considering you can only make one Mountain Peak per run, you may want to hold on to your mountains or face those nasty monsters.
It may take a while to unlock Forest and Thicket cards, but when you do, you can place a Storm Temple next to them to create Burned Forest. The Burned Forest gives you 0.5 extra magic damage per arson. And in case you didn't know, magic damage bypasses enemy defense, and while it can destroy tankier enemies easier, it's a very situational buff.
Blood Groves can only be placed next to a Grove. What happens if you obliviate a Grove from existence? Exactly, you get a Hungry Grove. It functions the same way as the Blood Grove but does more damage to both parties in battle and now instantly devours enemies under 20% HP. While the risks are greater, so are the rewards. Also, placing a Blood Grove next to a Burned Forest will instantly create a Hungry Grove. Burning the Forest later on also works.
Oasis is one of the best tiles because its benefits severely outweigh its prejudices. By placing a river card next to a sand tile, you will get an Oasis. This tile decreases our hero's attack speed by 1% but in exchange, it decreases all other creatures' attack speed by 2%. Everyone suffers, but your enemies suffer harder.
The easiest to create and one of the most powerful tiles in the game. You may have read somewhere else that you need to put a Meadow next to a Mountain, Rock, or Treasury. They are fooling you! A Meadow next to any card except itself becomes a Blooming Meadow. Ok, I can't confirm if next to ALL cards, because I'm not that far away into the game, but I tested with many. The card recovers 3 HP each day and is essential for our heroine to stay on her feet while looping endlessly.