Overview
From the start, you should decide whether you'll get Skypiercer. If you're unsure, you can buy an axe for faster farming and higher damage in battles. (Important note: if you have Granger on your team, picking Martis isn't the best choice, as these heroes clash very strongly.) It's worth mentioning that Skypiercer is very important for this hero, as his abilities synergize very well with it. The Trident is a very useful item, allowing Martis to kill enemies much more easily. It reduces the chance of losing his ultimate.
Strengths
The hero has incredibly high damage, and he also has the ability to not receive incoming control, which allows him to stay in battles longer.
Weaknesses
Martis's main problem is his slowness before his ultimate. Any hero with proper map play will avoid this hero's clutches.
Item
You can change the last three items at your discretion, but at best all three should be defensive. (Since Martis is very poor in full damage.) You might also consider purchasing a "golden meteor." Of course, it all depends on the situation on the map.
Rush
This combination of emblems is the most stable and strongest for this hero.
Battle Spell
Basically, it's worth taking blue retribution on the hero "Martis", but in some cases, red is also suitable.
Best With Granger
20% co-op win rate
The thing is that both heroes need to kill, which causes conflicts and makes it difficult to implement.
Watch Out For Floryn
40% counter win rate
Any gear with regeneration for allies can be a problem for Martis. It's worth keeping in mind that even a built-in anti-healing item won't always help.