Toski, porteur de secrets

A spell or ability that counters spells can still target Toski. When that spell or ability resolves, Toski won't be countered, but any additional effects of that spell or ability will still happen.

If Toski can't attack for some reason (such as being tapped or having come under that player's control that turn), then it doesn't attack. If there's a cost associated with having it attack, you aren't forced to pay that cost, so it doesn't have to attack in that case either.