Basic Combat Guide.
So the game deviates from the standard turn based combat where a character only gets to do one action per turn. In Curse Errant your turn doesn't end until you press standby, which means you can activate every single skill till you run out of TP and or everything is on cool down. So efficient TP management is the most important thing. The only exception to this is when you use one of the element cards which instantly ends your turn, so use any skills you want before hitting standby or using an element card.
Beyond just buying the newest sword and belt in every village. Early in the game just farm wolves / boars till you get to like level 10 or something. Where you unlock the Pin Down skill (80% chance to gain 30 TP), and Knights Prayer (Heal 30% health and gain 50 TP). Once you get those 2 skills combat basically becomes a non issue because you can usually wipe out most enemies before they even get to attack you. Since you essentially have a guaranteed 100 TP (starting 50 TP and the 50 TP from using Knights Prayer), and high chance of having 130 TP if Pin Down's bonus TP procs.
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Till you get the end game Rune called Passion the Dragon Sanctuary (or NG+) which gives passive High Spirits, you always basically want to activate the Excitement skill on your first turn if you're attacking to get the High Spirits buff for 1 turn. Not sure what the exact effects of High Spirits is but it seems to just give you a flat damage bonus of something around 20%-25%.
Then just spam Powerful Strike till all the enemies are dead. For almost all the common enemies usually 1-2 hits from Powerful Strike is enough to kill them. With Knights Prayer, where you basically have 100 TP, you basically always going to be able beat every encounter without ever taking any damage since you can use Powerful Strike 4 times in the first turn, 5 times if you use Pin Down and get the bonus to proc. If you have the end game rune called Hatred that reduces TP cost by 10, you are able to attack 10-13 times on the first turn, which is more than enough to kill any bosses.
On the rare occasion where you need a second turn to defeat an enemy, you then want to use the Full Force Strike for your first attack to get High Spirits again since Excitement is on cool down, then just use Powerful Strike for your following attacks. Powerful Strike does like 10% more damage than Full Force Strike.
Very rarely do you encounter more than 2 enemies at a time in a battle and to be honest I think you ever encounter at most at most 3 enemies at a time. That is when want to use Sweeping Strike, which attacks all enemies. It is pretty weak compared to Powerful Strike and usually takes 3-5 attacks for common enemies. Cause you won't have enough TP to do 6 Powerful Strikes (2 per enemy) which cost about 150 TP, while you usually only have 100 TP or 130 TP if Pin Down's bonus procs.
Unless you have played the game before or save scumming this next tip isn't very useful since you won't know when to do it. There is only like 1 or 2 instances where a boss has more health than you can shave off in your first turn. In that scenario it is better to just immediately use standby to get another 50 TP, so that you have a full 100 TP before you activate Excitement and other skills, so that you can maximize damage from High Spirits. Where you get 6-7 Powerful Strikes with High Spirit's damage bonus instead of just 4-5 during your first round of attacking (150 / 180 TP instead of just 100 / 130 TP).
Though this also applies when you are about to use Full Force Strike, where you know a single Full Force Strike and Powerful Strike isn't enough to finish the enemy in your second turn, or that it will take more than 2 Powerful Strikes in your third turn while Excitement and Full Force Strike is on cool down.
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As long as you have farmed enough gold in the previous area to buy the newest sword and sword belt in the next village you don't really need to worry about Runes or Accessories or element cards for basically the entire game. Runes and Accessories offer such minor stat boosts, and as previous said you basically can nuke any enemies you come across during your first turn if you took my advice to level up to like level 10 early on to get the Knight's Prayer and Pin Down skill. By farming enemies for gold you, should already have enough passive attack increase from your levels to not nude runes or accessories. Most of the time the sword you can buy or get from the quest is already good enough to farm the enemies in the area you're at, especially since they either give you a no element weapon or the element that the enemies in the area are weak to.
In my first play through only 2 bosses took more than 1 turn to beat or even posed a moderate threat.
Grumaji (the ghost boss in the library) and the boss to restore the magical sword. With Grumaji he just has a lot of health early game but it only takes like 2-3 turns to defeat him (especially if you do the standby tip mentioned above), he is not really a challenge.
The restoring the magical sword dark spirit boss named Flam, all you need to do buy either 2 blue cards or 2 white cards or 1 of each since Flam is weak to water and thunder. You only need like 3 turns of attacks worth of damage to beat it, but if you don't do my standby tip to maximize damage from High Spirits in between turns then you might need 4-5 turns. The cards give you the element bonus for 3 turns, so 2 cards for a total duration of 6 turns should be more than enough.
Flam is the only enemy where you need anything special other than your already equipped sword and sword belt to beat. The special equipment is a laughably low threshold 2 cards as previously mentioned.
So no need to min max with equipment or waste time farming components for runes or a lot of unnecessary gold.
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Element bonuses and weakness do not stack (additively or multively) and usually only checks for one thing and applies to the player's benefit. As in the game only checks if you have at least opposite element is present during attack rolls and if you have at least one of the same element is present.
What does that mean?
When you have the opposite element as the enemy you do 150% damage to them, in other words a 50% damage bonus.
When you have the same element as the enemy you both only take 50% to each other, in other words a 50% damage reduction.
For example the magical sword spirit named Flam has the fire and darkness element. You are forced to use they decayed magical sword which also has the fire and darkness element.
Without using any cards, you and the spirit both take 50% damage from each other.
If you use a blue a card, you start dealing 150% damage to Flam, while Flam still only does 50% damage to you. Having both fire and water elements doesn't cancel each other out, but rather gives you the best of of both worlds.
If you use a blue card and white card to give yourself both the water and thunder elements at the same time. You're still only going to be doing 150% damage. You are not going to do 200% (if bonus the stacked additively) or 225% damage (if the bonus stacked as a multiplier). You're only going to get a single flat 50% damage bonus as in doing 150% damage.
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Last misc tips.
When going into areas with enemies as long as they bump into you from the front or the sides, you basically always get to attack first. If they bump into you from behind they get to attack first. So avoid letting enemies bump into you from behind if you don't want to let your armor get damaged.
The armor repair potion repairs for 20 AP per use, so no need to wait till Giselle's armor is super low to repair. You probably only need to use like 2 repair potions in a play through if you want to keep Giselle's armor in pristine condition the entire time. Once you get the manuscript from the Library, you get one free repair when you head back to Sharon. Or if you complete the quest to help Derick's back pain you get free equipment repairs after you spar with him. Though to be honest they cost like 10 gold, and you find like 5-6 for free. So not really a big deal.
You can all flee at any time for no penalty except during boss fights.
The defeat option is mostly pointless since most of time enemies don't have any sex scenes, just knocks out all your health.
Have Lana buy meat for Giselle in Harbor City to give her the permanent +5 attack. Cause all the other stats are basically worthless if you kill enemies before they ever get to have a chance to attack.