Great Weapon Master trigger

Hi - I may  be overlooking something, but is there a way to trigger an additional attack roll if I roll a critical on a GWM attack?  On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.

Hi Brewksy McDain, Which character sheet are you using? If you don't know the name please supply a screenshot. 

Its the D&D 5E by Roll20

Short of an API script event your best bet is to put a Chat Menu button in the attack.  To do that:  Drag the attack to the bottom of the character sheet Press the macro button that is created.  Click on the Chat tab Click on the box where you type in the Chat tab.  Hit the Up Arrow on your keyboard.  Copy the command in the Chat tab box.  Go back to the attack, edit it (click the cog).  In the description put: [Desired name](~copied text) Remove the characters "%" "{" and "}" (without quotes) from the copied text.  Close the edit (click the cog again) and test.  Finally, hover over the macro button that was created, grab the handle on the right side, pull the handle up towards the top of the game to remove the button. 

I don't seem to get a chat tab or option to dump the syntax into a macro. After a drag out for a macro it doesn't even show up in my macro list in the pulldown menu? 

Brewksy McDain said: I don't seem to get a chat tab or option to dump the syntax into a macro. After a drag out for a macro it doesn't even show up in my macro list in the pulldown menu?  Alright, going to use some visuals:  Step 1: Drag the attack down to the bottom of the character sheet as shown.  Step 2: click the button it creates Step 3: click the Chat area where you type (#3) and hit the up arrow on your keyboard. Highlight and copy the text.  Step 4: Hover over the attack and click the "cog".  Step 5: in the description put [If Critical push me! (bonus attack)](~copied text) Where copied text is you pasting the command you copied from step 3.  Then remove the %{ and } from the copied text.  Step 6: Click the cog again Step 7: Click the attack, note that the output in the chat. You may push that grey button and it will make another attack.  Step 8: Hover over the button at the bottom, a little handle will appear on the right side...grab it and move it towards the top of the screen. 

Thanks!