Leylines are entirely influenced by the environment. For example, in deserts or arid climates, the water element will be penalized, while in coastal areas, it will be boosted. Each area within a location features different environments, but the map graphic provides a helpful guide to determine which locations to avoid as a Hydromancer and which to explore more closely.

In practice, this means you won’t find any location where both Fire and Water are boosted simultaneously. Your best option is to seek areas where either element is boosted or where neither is penalized.

The early game is really a slog for pure magic characters. Between leylines and no gear, and the enemies that steal money I die all the time. You might want to look at the balance here unless you know magic is hard mode on purpose. No gear, no option lots of clunky save scumming.
I beat the game many times with other archetypes.

EDIT: I fail to see any logic in leyline water aversion. It is virtually everywhere. Please start a hydromancer and see for yourself. The only options are grinding starting zones. You can't expect players to have 2 decks so early and every start should be equally viable and fun.

Magic isn’t inherently difficult, but the build you’re aiming for here is contradictory. Playing with both Fire and Water elements simultaneously means that one of your elements will always be penalized, as there are no leylines that benefit both. This approach can offer versatility, but only if you create two separate decks—one for Fire and one for Water.

In comparison, combinations like Fire/Air or Fire/Earth, or any pairing that isn’t inherently opposing, would be more synergistic. Additionally, your species determines your starting location. For example, choosing a species that lives in a desert and building them as a Hydromancer will make things significantly harder due to environmental penalties.

Finally, you can travel. If you’re playing with elements that have bonuses and aversions, it’s crucial to choose your locations strategically. Use Imbue wisely—it can double your bonus or penalty, or even negate it altogether.

Other archetypes, such as slashing or piercing, are generally easier to play since they typically lack bonuses or penalties. However, the tradeoff is that most enemies tend to resist them.

I chose a Nereid... Water creature by excellence and I'm popping up in the middle of a desert!
Building 2 decks does not seem contradictory because either water or fire is penalised, so at some point I could have been geared for both terrains although I would still have favored water. I also planned Seduction as a side gig.
I immensely enjoyed the game in the past years but this leylines mechanic and awful start (please no enemies stealing money in a starting zone when I NEED to buy gear...) made me give it up this time.

Nereids begin in Tethyar, except in certain game modes where the starting location is randomized. From what I recall, this applies primarily to Constructed mode, where you don’t keep your starting deck, and it is classified as a Difficulty 5 mode. Alternatively, this can happen when ascending to a + mode.

Leylines are designed to be both a challenge and an advantage. Your starter deck is sufficient to navigate the early game, though in Constructed mode, you’ll need to build that deck yourself. With a solid understanding of the mechanics, leylines can become a significant boon for elemental users.

If you’re experimenting with a new archetype after a long hiatus and finding it difficult, I’d recommend starting in an easier mode to regain your footing.

For a milder Constructed experience, you might consider sticking with a Nereid Hydromancer in Collector mode. Starting in Tethyar, you’ll have a smoother progression and can build your secondary specializations as you advance.

Well everything that is not the starting zone is anti-water around Tethyar. Never mind.