
Your both nuke and enemy repositioning spell. It's already a good spell by itself, but it is also what enables Mars as a support.
Things to note:
- If you fail to pin your target, it will be facing you afterwards
- It allowes you to see invisible units and ives vision
- Only gets targets to the front, it won't catch a hero standing right near your model

Another spell to mess with enemy positioning, but also a nuke and a farming spell.
Tips:
- It can interrupt forced movement, including your own spear
- You can proc all attack modifiers, but cooldown based ones (bash, maelstrom) won't proc more than once
- It attacks targets from left to right, so with basher the most right target has higher chance to be bashed
- Damage pierces BKB

Your main spell for tower diving and early brawling. It gets only better with levels and items, so it's not worth maxing it early on.
Tips:
- Reduces only PHYSICAL ATTACK DAMAGE and attack damage like abilities (Monkey King's Q), but not from Swashbuckle
- Block works as usual: doesn't stack, blocks after armor

Your great teamfighting spell and synergy enabler for everything you have. Use it to catch your enemies and control their positioning to then later kill them with Spear+Rebuke
Tips:
- Doesn't pierce spell immutiny
- There may be multiple arenas
- Mars and teammates can get in and out freely
- It's possible to get out with instant movement (blink) or manipulation with Z axis (Toss+Force Staff, Pounce...)

It can be very strong and make you and your team hard to take down. It may work great in lategame scenarios or just while pushing enemy highground in general
Early
Cheap flat mobility bonus, to be upgraded into drum later
Core
ALTERNATIVE: Drum of Endurance, Vladimir's Offering
Situational Early
Main mana sustain item. Enables Mars as a farming hero between fights, but also allowes him to fight more often considering his manapool
ALTERNATIVE: Arcane Boots
ALTERNATIVES: Eul's Scepter of Divinity, Vladimir's Offering
Utility
Buffs your whole team, but also makes you way more tanky (because of lifesteal and God's Rebuke interaction)
ALTERNATIVES: Eul's Scepter of Divinity, Drum of Endurance
Situational
Cheap and efficient damage/farm solution for Mars. Good for agressive games when you're way ahead
Status resistance, tankiness and instant heal from God's Rebuke
For cases when you tank a lot or as a desperation move
Other Significant Items
If you feel like you have a lot of money, you can go for Atos. It's great item for Mars stats wise (a lot of strength and massive manapool increase) and relatively cheap, so it's affordable even for a support Mars