on PC there is a lock symbol at the top right that must be checked before you can lock and unlock individual items. i don't know about mobile.
What do you mean you can unlock it, how???...It says you can't take it to the trader?Of course you can sell it. There was an update a while back that new special buildings are locked by default so players don't accidentally sell them and then submit tickets to get them back. You can unlock it and sell it.
As for the event: same as last year. Hopefully the building is easy enough to complete (even though the def boost is approaching useless) without specific play style or lots of luck. The tournament is silly like last time: with most odds in the 30-70% chance to win, and the relatively small # of tickets available the "strategy" component is easily swamped by randomness. Just do the hard match--swap players if you like--and don't save up tickets for prizes there as you lose out on the generated ones.
I'm starting to get burned out on events, particularly because of the complete [x # of y time] production quests which seem to be more obnoxious with each new event. My main world has a fair # of sleigh builders so it isn't so bad, but on others I only have a few production buildings (including whatever smiths I can shoehorn in there) and if you have to wait through multiple cycles of 8 hr productions...it's just a drag.
And on mobile the line at the top has 3 check boxes to the right of the search area. Tap/select the one on the right and your inventory items will all show check boxes below to toggle items between locked and unlocked. When you're finished, deselect the lock box at the top.on PC there is a lock symbol at the top right that must be checked before you can lock and unlock individual items. i don't know about mobile.