It took me a bit to figure out that the number keys are used to choose the action (grenade, summon skeleton and scarecrow), maybe include that in the description.

I liked how the scarecrow sucks in the goblins. I feel like the grenade could have a bigger area of effect. Also, a background would have helped to make the speed and direction of scroll more clear.

It would be nice to have a score or some kind of objective (it seems like it never ends). Overall a good idea that just needs some tweaking to make it great!