Re: (Corn)What exactly is butter beacon? what does it do?

It highlights enemies in the area for the duration of the effect, even through walls and other obstacles. 

While enemies are highlighted by the beacon, your cob busters do slightly increased damage (a crit is 6 instead of 5 for example).

You get some XP for enemies vanquished by teammates in the area of effect of the beacon, it's called butter support or something like that.