
Legendary Artifact
Spells you control can't be countered.
At the beginning of your end step, discover 5. (Exile cards from the top of your library until you exile a nonland card with mana value 5 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

Colorless artifact providing repeatable value engine to any deck.

Cheap colorless artifact protecting spells from being countered.

Protects your spells from interaction during your turn.

Free top-of-library cast value each turn, similar discover payoff.

Big colorless threat whose spells can't be countered.

Cascade-style free spell value generator.

Colorless utility commonly slotted into any color identity deck.

Cheap artifact taxing counterspells to protect your plays.
Chimil, the Inner Sun's first ability applies only while it's on the battlefield. While it's a spell, it can be countered.
A spell or ability that counters spells can still target spells that can't be countered. When that spell or ability resolves, the uncounterable spell won't be countered, but any additional effects of the countering spell or ability will still happen.