Macro for conditional damage weapons

How do you make a macro for weapons like the Lightbringer or the Dragonslayer longsword? I need help to program the macro for when the weapon hits an undead or dragon, respectively, then does extra damage. 

Depending on the sheet/system being used you can often put conditional stuff as part of the attack description for quick reference should the criteria be met. There are potentially other, automated, ways to handle it but that would depend on the sheet etc and may also result in having to answer a query EVERY time the weapon is used which might get annoying if most of the time the answer is 'no'.

If its a longsword and the 2handed damage die is in the second damage window you can put the conditional damage as a [[1d10+X]] in the description field with some conditional text explaining what its for.  

What's the code for that?

Assuming you're using the 'D&D 5E by Roll20 Sheet', For the Lightbringer, you can adjust a +1 mace and add this to the 'DAMAGE2:' field: ?{Undead?|No,0|Yes,1d6 [Against Undead]} For the Dragonslayer Longsword, you can adjust a +1 longsword and add this to the 'DAMAGE2:' field: ?{Dragon?|No,0|Yes,3d6 [Against Dragons]}

Totally never occurred to me to put a query into the damage field like that.  Though if its a DM doing this, may want to ask the player in question first as I have a few players who despise queries in their spam attack keys, its usually fighters that complain about it.  If a player doesn't want a query, just put "**[[3d6]]**  additional damage if dragon."  in the description field where Jarren's image says "Up to 2 creatures within 5 feet" message.  

Much appreciated.  Jarren said: Assuming you're using the 'D&D 5E by Roll20 Sheet', For the Lightbringer, you can adjust a +1 mace and add this to the 'DAMAGE2:' field: ?{Undead?|No,0|Yes,1d6 [Against Undead]} For the Dragonslayer Longsword, you can adjust a +1 longsword and add this to the 'DAMAGE2:' field: ?{Dragon?|No,0|Yes,3d6 [Against Dragons]}