Does a spell count as cast if its countered?

Yes, the spell is cast. This will count for “on cast” triggers, Storm, Aetherflux Reservoir, Approach of the Second Sun and Commander Tax.

What happens when a spell is countered?

701.5a To counter a spell or ability means to cancel it, removing it from the stack. It doesn’t resolve and none of its effects occur. A countered spell is put into its owner’s graveyard. 701.5b The player who cast a countered spell or activated a countered ability doesn’t get a “refund” of any costs that were paid.

Does prowess trigger if spell is countered?

Prowess goes on the stack on top of the spell that caused it to trigger. It will resolve before that spell. Once it triggers, prowess isn’t connected to the spell that caused it to trigger. If that spell is countered, the ability’s effect will still resolve.

Does counterspell use a spell slot?

No, if the spell did not take a slot to cast Some classes, such as Warlocks and Monks, can attempt to cast spells without using spell slots. But counterspell still has the potential to stop those spells. Also, counterspell could counter a spell cast as a ritual, in which case, again there are no spell slots involved.

Can force of will be countered?

Force of Will cannot counter abilities, so it cannot prevent AEther Vial from putting a creature onto the battlefield.

Can you buy back a countered spell?

Buyback returns the spell to your hand only if the spell resolves. If the spell is countered, it goes to the graveyard as normal. If you control a copy of a spell whose buyback cost was paid, the copy will be put into your hand as it resolves, then it will cease to exist.

Does a failed spell use a slot?

If your concentration is broken, the spell fails, but you don’t expend a spell slot. If you want to try casting the spell again, you must start over. Because of the mental focus and precise gestures required for spellcasting, you must be proficient with the armor you are wearing to cast a spell.