Atraxi Warden

If the second triggered ability is countered, the card can't be cast. It remains exiled with no time counters on it, and it's no longer suspended.

When the last time counter is removed, the second triggered ability of suspend (the one that lets you cast the card) triggers. It doesn't matter why the last time counter was removed or what effect removed it.

If the card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

Exiling a card with suspend isn't casting that card. This action doesn't use the stack and can't be responded to.

If an effect refers to a "suspended card," that means a card that (1) has suspend, (2) is in exile, and (3) has one or more time counters on it.

If the first triggered ability of suspend (the one that removes time counters) is countered, no time counter is removed. The ability will trigger again at the beginning of the card's owner's next upkeep.

Cards exiled with suspend are exiled face up.

If the spell requires any targets, those targets are chosen when the spell is finally cast, not when it's exiled.

The mana value of a spell cast without paying its mana cost is determined by its mana cost, even though that cost wasn't paid.

Due to a recent rules change to suspend, you are no longer required to cast the suspended card as the second triggered ability of suspend resolves. Instead, as the second triggered ability resolves, you may cast the card. Timing permissions based on the card's type are ignored. If you don't cast the card, it remains exiled with no time counters on it, and it's no longer suspended.