Quicksilver Sea — ruling 1

You play the card (meaning it play it if it’s a land card or cast it if it’s a nonland card) as part of the resolution of the chaos ability. Timing restrictions based on the card’s type are ignored. Other restrictions, such as “Cast [this card] only during combat,” are not.

Quicksilver Sea — ruling 2

If you reveal a land card when resolving the chaos ability, you may play it only if you haven’t played a land yet that turn.

Quicksilver Sea — ruling 3

If you cast a card without paying its mana cost, you can’t choose to cast it for any alternative costs, such as evoke or the alternative cost provided by the morph ability. If it has {X} in its mana cost, X must be 0. However, you can pay optional additional costs, such as kicker, and you must still pay mandatory additional costs, such as the one on Fling.

Quicksilver Sea : règles, fonctionnement et interactions (MTG)

Quicksilver Sea is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

When you planeswalk to Quicksilver Sea and at the beginning of your upkeep, scry 4. (Look at the top four cards of your library, then put any number of them on the bottom and the rest on top in any order.) Whenever chaos ensues, reveal the top card of your library. You may play it without paying its mana cost.

How it works : Quicksilver Sea

Original English text — Wizards of the Coast / Scryfall

#1June 1, 2012· Wizards of the Coast
You play the card (meaning it play it if it’s a land card or cast it if it’s a nonland card) as part of the resolution of the chaos ability. Timing restrictions based on the card’s type are ignored. Other restrictions, such as “Cast [this card] only during combat,” are not.
No other card is named in this ruling.
#2June 1, 2012· Wizards of the Coast
If you reveal a land card when resolving the chaos ability, you may play it only if you haven’t played a land yet that turn.
No other card is named in this ruling.
#3June 1, 2012· Wizards of the Coast
If you cast a card without paying its mana cost, you can’t choose to cast it for any alternative costs, such as evoke or the alternative cost provided by the morph ability. If it has in its mana cost, X must be 0. However, you can pay optional additional costs, such as kicker, and you must still pay mandatory additional costs, such as the one on Fling.
No other card is named in this ruling.