Lots of theories on how to deal damage and what stat affect what is out there and most seem faulty so I decided to test it out.
Various moves do different kinds of damage, keeping track of what your weapon does best, boosting corresponding stats and hitting the sensitive spots do wonders for damage output.
On the various weapons: Damage does not follow the pattern of 50%STR +Impact modifier with DEX for thrust, STR for strike and AGI for slash. It is mainly false on the STR as base part. AGI often follow Slash and so on but not always and many moves are AGI/DEX, AGI only and DEX only. Spear moves may use VIT and Staff moves SPR. Most elemental moves include INT and one other stat. No move seems to rely on more than two stats.
One-handed: STR/AGI/DEX Short sword has several moves for all three categories and use all the three weapon stats fairly equally but I set STR/AGI as the main ones. Look for what kind of damage the move does and you get the stats to boost it pretty accurately with the normal AGI for slash, STR for strike, DEX for thrust and INT for elemental. Note that 1-H have 3 kinds of weapons (who are sorted separately in the storage.) The normal swords and the fast daggers are both slashing weapons (as in they ad slash damage to combos) while the axes/cleaves are strike weapons. 1-H can thus make breaking combos of both slash and strike moves. Use this to your advantage when setting combos and dressing up. Try use strike moves/combos and STR gear for axes/cleavers and slash moves/combos and AGI gear for swords/daggers. Learn what enemies are weak to what and where and you'll kick some ass as one handed too.
Longsword: AGI/STR/DEX Most useful moves are slashing and AGI is the main stat here. STR and to a lesser degree DEX is also useful. AGI also enhances your chances of evading enemy attacks and that’s very useful since the Longswords lowers your VIT.
Axe: STR/DEX (AGI) Most moves are strike and it’s STR all the way for most moves. Some moves use DEX and a few AGI but I would not bother with AGI.
Spear: DEX/VIT/AGI DEX appears to influence damage on all spear moves, AGI and VIT influence some. The widely held belief of 30%STR+ 40%VIT +30% Slash/Strike/Impact modifier is false. STR appears to have no impact on Spear damage what-so-ever regardless of move. Extensive testing have given the following: Not all Spear moves have VIT as damage modifier and DEX appears to be a stronger one when it is. Most notably VIT influence damage on heavy damage dealing moves like Dart and Pentaslam. AGI influence damage on the slash moves. Notable is also that INT does not influence the ice elemental moves who appears to be DEX only. Conclusion is DEX and VIT with some AGI for most damage.
Bow: DEX/INT (STR) Different moves have different modifiers with only some logic behind it. Extensive testing have given the following result: The damage modifiers does not follow the normal settings at all but move stated as strike, slash or thrust do increased damage on corresponding weak spot as normal. Sting: 50% STR/50% DEX Bull’s Eye: 50% INT/50% DEX Blast Tip/Blast Salvo: 100% STR Double Nock/Triple/Knock: 100% DEX Needle 100% DEX All Elemental Tips/Bolts 50% INT/50% DEX If its DEX or INT that's most important can be discussed but INT builds seems more popular among high GR players.
Staff: SPR/INT The elemental moves are 50% SPR +50% INT regardless if they’re strike, slash or thrust. Main damage increasing stats are thus SPR and INT. The seeker elemental boost will increase damage on corresponding elemental move. A correctly built and played staff can do massive damage.
On combos: INT does not increase combo damage other than for moves that normally have INT as modifier i.e. most elemental moves. You need 4 moves to get a combo complete. With the right weapon and moves that may cost you only 3AC. The combo complete bonus it appears is not that complicated after all, actually its one of few things in this game that is consistent and predictable once you figure it out. Also it's a complete no-brainer. The percentage is always the same for any given combo regardless how it is constructed, of enemy weaknesses and you button mashing it or not. 4 moves is needed to make combo complete a 4 move combo have 25% damage bonus. Any excess moves will lower the percentage according to this simple formula: 4/(total moves in combo)*25% and thus: 4 move combo -> 25% bonus 5 move combo -> 20% bonus 6 move combo -> 16,66% bonus 7 move combo -> 14,28% bonus Which means the bonus is just the average of all moves in the combo.
Making a combo that makes more than one combo complete (i.e both thrust and an element modifier reaches +10) does NOT ad extra damage to the combo complete. Some personal opinions on combos: Moves that cost lots of AC (like deadly fang) are generally not worth the cost. More than 6AC in a combo is an AC-waster and should only be used for all out assaults that is aimed to kill a boss/foe very quickly.
On elemental weapons: An elemental move cancels whatever element your weapon have and deal ONLY damage according to the element of the move and NOT the weapon. An elemental move will NOT get stronger if you use a weapons of the same element. Adding only +1 of an element to a weapon will give the full elemental damage bonus for every move. It will also reduce the damage of all moves but the elemental moves should it be used on and enemy strong against the element. Adding more than +1 of an element ads NO extra damage and is only useful if you want to make a combo complete using the elemental modifier. In practice I find that mostly bows and staffs have good use for this. Other weapons usually makes combo complete way easier in other ways.
On the enemies: Two things monster-wise decide your damage, their weaknesses and their DEF. DEF is the same all over but nothing in this game is simple and consistent some weak-spots are more weak to certain kind of damage than others. The hidden bellies of most four legged enemies are extra weak to thrust and slash but not to strike. Heads of Trolls and Giants are extra weak to strike. The back of Spiders and the torso of Greavers are also extra weak to thrust and slash.
Have made a list here of all big enemies and their weaknesses. I made this a while ago to have as a quick reference when playing. Think most, if not all this info is already in the wiki but here you got it all in one page.
Dragons: Legs: No weakness Belly: Weak to strike, EXTRA WEAK to thrust and slash. Back: No weakness, may give break drop. Head: Weak to slash, strike and thrust. Tail: Weak to slash, may give break drop. Aged dragon is strong against all elements and the other have the obvious elemental weakness/strength.
Awahee: Legs: Weak to strike. Belly: Weak to strike, EXTRA WEAK to thrust and slash. Back: No weakness, may give break drop. Face: Weak to slash, strike and thrust, may give break drop. Weak to fire, strong against water.
Greavers: Legs: No weakness. Torso: Weak to slash, strike and thrust. Head: Weak to slash, strike and thrust. Tail: Strong to slash, strike and thrust, may give break drop. Normal greavers are weak to wind, strong to earth. Toxic Greavers are weak to fire, strong against water.
Cerberus: (Fire-Beast) Legs: Weak to slash. Belly: Weak to strike, EXTRA WEAK to thrust and slash. Head: Weak to slash, strike and thrust. Heads on back: Weak to slash. Weak to water, strong to fire.
Megalo Tigris: (Earth-Beast) Legs: Weak to slash. Belly: Weak to strike, EXTRA WEAK to thrust and slash. Back: No weakness. Head: Weak to slash, strike and thrust. Weak to earth, strong to wind.
Giant Spiders: Legs: Weak to slash. Belly: Weak to thrust. Back: Weak to strike, EXTRA WEAK to thrust and slash. Head: Weak to slash, strike and thrust. Direspiders are weak to wind, strong to earth. Waterspider, weak to fire, strong to water.
Trolls: Legs: Weak to thrust. Head: Weak to slash and thrust, EXTRA WEAK to strike. Belly: Weak to slash, strike and thrust. Normal Trolls are weak to wind, strong to earth. Troll-Kings are weak to earth, strong to wind.
Giants: Legs: Weak to thrust. Belly: Weak to strike, slash, thrust. Head: Weak to slash and thrust, EXTRA WEAK to strike. (Obvious elemental weakness/strength)
Golems: Weak to strike all over. All golems are strong against earth. Clay is weak to wind, Stone is weak to water, Iron is weak to fire and Gold is strong against all and have higher DEF.
Knave: Weak to strike all over. Heads are extra weak to strike. No elemental weakness or strength.
Treant: Weak to strike all over. Weak to fire, strong against wind.
Gigas: Legs: Weak to slash. Belly: Weak to thrust. Head: Weak to strike. No elemental weakness. Some, like those that throw spells at you like Betapente, are also strong against all elements.
Grand Gigas: Legs: Weak to slash. Belly: Weak to strike, EXTRA WEAK to thrust and slash. (Extra weakness not confirmed) Head: Weak to strike, slash, thrust. Heads on back: Weak to slash. No elemental weakness or strength.
Pyredaemus: Legs: No weakness Belly: Weak to strike, slash, thrust. Head: Weak to strike. Turret. Strong against strike, slash and thrust. Weak to water, strong against fire. You need to break both legs on one side to tip it. Breaking two legs on opposite will sides make it kneel down only making the head reachable for ground based attacks.
Pyredaemus Rex: Legs: No weakness Belly: Weak to strike, slash, thrust. Head: Weak to strike. Turret. Strong to strike, slash and thrust. Strong against all elements and have higher DEF. You need to break both legs on one side to tip it. Breaking two legs on opposite sides will make it kneel down only making the head reachable for ground based attacks.
Laima Comitis: Legs: No weakness Belly: Weak to strike, EXTRA WEAK to thrust and slash. (Extra weakness not confirmed) Back: No weakness, may give break drop. Head: Weak to slash, strike and thrust. Tail: Weak to slash, may give break drop. Strong against all elements. You need to break both legs on one side to tip it.
Some notes: The staffs Seeker elemental damage boost can be used for the corresponding elemental move with any weapon. You need however have a staff and 5AC on your hand when casting the seeker, switching weapons will NOT halt the damage boost for elemental moves. Bellies don’t have lower DEF. They usually have more weaknesses though. If you do slash damage and legs are weak slash you’ll do just as much or more damage on the legs. You can break a tail for drop even if an enemy is lying down. The Greaver torso don’t give break drops. The Megalo Tigris back don't give break drops. The Cerberus don't have a back to hit under the heads on its back. Robert is by far the most annoying NPC in the game.