The button for grappling is the left mouse button. We seemed to have that issue too originally with the build but we were sure to fix it before uploading and tested it on multiple devices and it worked. We are sorry for the inconvenience.
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We did consider that but we found that the game was too easy after a lot of trial and error we found that it started getting hard at the 100m range so we stuck with the current size. Thank you for the feedback though we will consider making changes according to your recommendation. Also in case you weren't able to figure out the full controls yet we made sure to update for now with a list on the page of the game and soon will be added inside the game menu as well. Thank you for trying our game and sharing your feedback.