Terminus is one of the strongest tank in the game with very high skill cap. The skill ceiling is so high that he is banned in the PPL. Luckily, for us plebians casual players, there is no one preventing you to play this character. So what are you waiting for, queue a casual game and ready to instalock Termimus!
There are certainly many good cards are viable to make a decent loadout of Terminus, you can steal all the builds from the pro players all you want. But what's the point of making a new loadout for Terminus anyway when you have already got a perfect default loadout build from Hi rez!
When the game starts, you just buy nimble instantly. Cauterize? Wrecker? Rejuvenate? Pffts that's what your teammates are supposed to do. Your only job is to trust yourself, buy nimble and carry your team. Nimble 3 is the most important item for Terminus so that you can walk to the enemy and swing your axe like a mad lad!
Ooof! You dive into the backline and got killed instantly (normally you would get penta kill but when the enemy team target you coz u were fragging so much, you may get killed). No sweat! After getting all the penta kills, you have already farmed ult charges. You need morale boost 3 as fast as possible as well so that whenever you die, you just press E instantly. Don't hesitate to press E whenever you die, even though all your teammate has died and you are in a 1v5 situation, you may end up getting a Penta kill with that, so why don't you take risk anyway!
You also need to buy master riding 3. Master riding is a crucial item as well. The enemy team thinks that you are feeding? Ho ho, they are just jebaited by you, because with master riding 3, you can return to the fight quickly and kill them all again!

Master Riding
Armor
Increase your Mount Speed by 45%.
Level 3

Nimble
Armor
Gain 21% Movement Speed.
Level 3

Morale Boost
Armor
Increase your Ultimate charge rate by 30%.
Level 3

Life Rip
Weapon
Your weapon shots gain +30% Lifesteal.
Level 3

Wrecking Ball
Shatterfall
Increase the leap distance of Shatterfall by 30%.
Level 3

Despoiler
Shatterfall
Heal for 300 for each enemy hit with Shatterfall.
Level 3

It Waits
Power Siphon
Reduce the Cooldown of Shatterfall by 0.8999999999999999s for every 1s spent channeling Power Siphon.
Level 3

Blood and Stone
Shatterfall
Gain 18% Power Siphon charge for each enemy hit by Shatterfall.
Level 3

Hulking Monstrosity
Armor
Increase your maximum Health by 450.
Level 3

Undying
Armor
Reduce the damage you take by 20% while at or below 50% Health.