There are different ways to research stuff for writing. In the recent months, I’ve realized there are things I can take from playing turn-based strategy games into writing fantasy combat.
RTS vs. Turn-based
Many of my initial ideas were shaped when I played Warcraft 3. Being real-time strategy, efficient management of details and reaction time can have a large impact and comparing troop movement is not really intuitive for long-term measurement. RTS is more active/fluid when it comes to playing but I admit it helped me none when it comes to understadning fantasy combat… especially in long-term outlook.
I’ve found turn-based strategy better in that aspect: each turn can symbolize a given time (day/week, for example) which helped me to get some idea about troop movement. You see a part of the battlefield and can consider several alternatives for each turn as one would their options when planning a battle strategy – because you have some idea how much ground can the troops cover per given time.
Rock, paper, scissors,… lizard, Spock?

In the simplest way, fantasy combat can be dumbed down to a RPS scenario: each type of troops has a strength that counters some of the other troops and a weakness exploited by another type of troops. And while it could be brought down to a trio (cavalry, infantry, archers – cavalry tramples infantry, infantry counters archers with shield wall, archers snipe cavalry), the reality is more complex even with the existing other troops (artillery, differences in durability between light- and heavy-armored infantry), let alone all the fantasy options (magi, elementals, dragons, monsters,…).

Even with all of that accounted for, there’s the aspect of landscaping: either natural or artificial roadblocks to allow/prevent a flanking maneuver or a wall to hold enemy at bay while ranged troops whittle them away.
Magic in fantasy combat
Another aspect is the power of magic: the skill of the involved magi, how many of them are willing to take part in the conflict (touches fictional politics, not the topic for today), and the limits of magic in a particular fictional setting. If I was to compare a mage to an archer: while archer’s attacks can be stopped by a shield wall, the effect of shield wall against magical attacks depends on several factors: what kind of magic can be stopped by a shield (which might differ for a shield made from wood or metal) and/or armor, the effective range of magical attack compared to an archer, the (in)existence of insta-kill spells, the (in)existence of anti-magic armor, and many others.
Likewise, it’s possible that a setting with the presence of magic would develop some way of countering it – either by most armies hiring magi to even the odds or by inventing indirect techniques of countering magic (such as my concept of Magic-Breakers, inspired by Warcraft 3’s Spellbreakers and real-life SWAT units) – and deployment of those units will again be affected by politics and the amount of people having those skills.
Stamina/fatigue can also have an impact on magi – and it’s likely to be tied to experience: an experienced mage will be able to use stronger spells and last longer than an apprentice. While its unlikely (but not impossible) for a mage to defeat an army alone in a story that aims for some degree of realism and balance, it can be done in the same scenario by clever use of environment (collapsing a bridge full of enemies might need less power than killing them all).
Monsters in combat
Another aspect of fantasy is the existence of fictional creatures ranging from humanoid to all kinds of beasts – and it’ll again depend on the setting which of those can be brought to a fight – and how. Even outside of battlefield, they are something to consider as adversaries of adventurers.
Some of them might be nothing more than durable infantry, capable only of melee strikes – such as an ogre or a giant – but the difference in durability can turn them into one-monster army. To use the RPS example again: where a conventional infantry would be countered by a cavalry charge, an orge or a giant might be resilient enough to withstand such an attack with minimal damage.
Likewise, the power of a dragon in fantasy warfare will depend on how far can their breath reach and their specific biology (flight speed, how many times they can breathe fire in a short timespan, how durable their scales are against conventional weapons, how vulnerable they are to magic, intelligence/will to be commanded…)

Likewise, elementals (if they exist in the setting) might have various (dis)advantages in battle – such as resistance to their own element but weakness to the opposite (fire elemental would be easier to defeat using frost magic, for example) but also their offensive skills and the (in)ability to use magic – whether they’re just partially-immune melee troop or a resilient ranged troop makes a huge difference.
One-man army
And when all of that is figured out, there’s the last major aspect: in many cases, the major characters are rule-breakers with various skill kits or wider options when it comes to their gear. A veteran warrior can be able to withstand much more just because their experience allows them to weather or avoid more blows than the average soldier can.

This difference in power can be even larger in case of magi: an apprentice might be able to only attack one enemy at a time and need several attacks to bring it down (unless their skills are a direct counter – such as the elemental example).
An experienced mage can have area-based attacks at his/her disposal, able to use stronger attacks or use their abilities faster. This is why writing a good combat scene with magic takes effort (and I respect anyone who pulls it out in a satisfying way): even the most powerful characters should have limits and weaknesses and they’re not always easy to write well. Furthermore, any weakness in the magic system can be exacerbated in a combat scene – either by creating an inconsistence, a plot hole, or lack of engagement due to lack of danger.
To wrap it up: writing a good fantasy combat is about more than just having a bunch of characters smack the living hell out of them – and was one of the most interesting learning curves I experienced (and I doubt I’ve reached the end of this curve). It’s something that can reveal weaknesses, inconsistencies, and plot holes within the setting and the magic system – or show the strengths.
As always, I’ll welcome your thoughts on the topic: if you are fantasy writer, what challenges did you face when writing combat scenes? What was a source of inspiration for you? If you are a reader, do you know a book with well-written fantasy combat? Or a favorite combat sequence? Feel free to share!
Screenshots taken from Age of Wonders III game.