A good little thing I keep in mind when choosing weapons against certain factions. There are three damage types; slash, puncture and impact that most weapons have. Some weapons excel in one damage type and aren't so effect against certain factions. An example; Slash damage is very good against infected enemy types, while it is terrible against armored grineer enemy types and shielded corpus types. I like to remember this when choosing weapon by their damage type for missions; slash for cutting flesh, puncture for heavy armor, and impact for shattering sheilds.
Now elemental damage is another bonus you keep in mind. Sometimes it's preference based on the effect a certain elemental combo will do. Either way, you sould always keep in mind to add elemental damage to your weapons, because it ADDS to the overall damage your weapon will do with one hit.
Each element damage mod gives an inherent effect to them when they proc on hit with a weapon. Note that there is a "Status chance" on every weapon, this determines the chance for whatever element a weapon has on it to take effect. The base elemental mods and their effects are:
-Fire- chance to cause fire damage over 6 seconds that is equal to 50% of your weapon's base damage and causes them to panic while the dot is active
-Electricity- chance to trigger a small AoE electric shock proc that is 50% of your weapon's base damage and stuns enemies for a short time
-Toxin- chance to proc a damage over time that is 50% of your weapon's base damage
-Cold- chance to slow an enemy's fire-rate and movement speed by 50% for 6 seconds
From these base elemental damage types there are elemental combos that further enhance weapon damage towards specific enemy types. Some of these elemental combos give some great late-game utility and offer great advantages against tough enemies. To get elemental combos you would place elemental damage mods and according to their order they would make the combo. The order is read from left to right, top to bottom, with innate elemental damage being read as the bottom most right position of your mod layouts.
Blast - Cold+Fire - Blast damage's status effect is an area of effect knockdown.
Corrosive - Electric+Toxin - Corrosive damage's unique status effect is Corrosion, which permanently degrades enemy armor by 25%, causing affected units to take more damage.
Gas - Fire+Toxin - does a Toxin AoE that deals 50% of your weapon or power's base damage in a small area around the affected enemy with a 100% status chance. As such, enemies damaged by this Toxin burst will also be affected by a Toxin DoT that inflicts 50% of the AoE damage per tick (9 ticks over 8 seconds).
Viral - Cold+Toxin - Viral reduces a target's maximum health to 50% for 6 seconds
Radiation - This elemental damage causes confusion, enemies under the effect will also be targeted by their own allies. It is similar to but less reliable than Nyx's Chaos ability. The status effect is visually noticeable as blue flashes on the affected unit.
Magnetic - Cold+Electric - When this damage type procs, the target's current shields and maximum shield capacity will be reduced by 75% over a duration of 4 seconds. After the effect expires, the target's shields and maximum shield capacity will be restored. Should multiple Magnetic status effects occur while one is already active, the duration will be extended, and the target's shields will be permanently reduced when the effect expires.
The damage system is pretty fun to play with once you get the elemental mods into the mix on weapons. Too bad most of the time you barely have space to put base damage...we need more catalyst alerts.