Card

Null Rod

Mana cost {2}

Activated abilities of artifacts can't be activated.

Part of 7 known combos, one of them two-card. 4 official rulings.

Bracket

B1 Exhibition — Not in the same deck as its two-card combo partner: Mycosynth Lattice
B2 Core — Not in the same deck as its two-card combo partner: Mycosynth Lattice
B3 Upgraded — Not in the same deck as its early two-card combo partner: Mycosynth Lattice
B4 Optimized — allowed: No restriction beyond the banned list
B5 cEDH — allowed: No restriction beyond the banned list

Bracket: Lotus Vault analysis, with Commander Spellbook flags

7 known combos, one of them two-card.

Null Rod + Mycosynth Lattice
Produces: Nobody can activate the abilites of any permanent on the battlefield, Activated abilities can't be activated, Lock
View on Commander Spellbook
Null Rod + Mycosynth Lattice + Archangel of Tithes
Produces: Nobody can activate the abilites of any permanent on the battlefield, You can't be attacked, Activated abilities can't be activated
View on Commander Spellbook
Lethal Vapors + Mycosynth Lattice + Null Rod
Produces: Activated abilities can't be activated, Lock, Mass Land Denial
View on Commander Spellbook

2016-06-08 · Wizards of the Coast
Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keywords are activated abilities and will have colons in their reminder text.
2013-07-01 · Wizards of the Coast
This effect does not prevent triggered abilities from triggering and it doesn’t stop the effects of static abilities.
2013-07-01 · Wizards of the Coast
This effect applies to all activated abilities of artifacts, including mana abilities.
2008-04-01 · Wizards of the Coast
This covers only artifacts that are on the battlefield.

Rulings: Scryfall · Wizards of the Coast