An effect can be added to an existing power or if no power exists a new one can be created. In the player Character sheet effects are created in the actions tab. For more details see the 5E NPC Sheet and the section below on the wording used to create NPC effects. Again, not everything will create an effect either because one isn't required or Fantasy Grounds doesn't have a way to create one.

Most of the standard NPCs from the Monster Manual will, when dragged to the Combat Tracker, create any necessary effects so that the DM can use them. This action causes Fantasy Grounds to attempt to parse the information contained in the NPC sheet and create the effects. In the case of NPCs effects appear on the Combat Tracker when the NPC is placed there either from the NPC list or from an encounter. For more information see the 5E Character Sheet As another example the spell 'Counterspell' won't create an effect either because Fantasy Grounds can't know what the difficulty class of the incoming spell might be. For example the spell 'Animal Messenger' doesn't require an effect since this spell and others like it are simply 'Theatre of the Mind' spells. Where an effect is not created via this method the probability is very high that either the spell doesn't require an effect or Fantasy Grounds doesn't have a built in way to handle whatever the spell is trying to do. For example dragging spells into the actions tab will in almost every case create an effect. Many effects are created automatically for you in the 5e ruleset by dragging and dropping from the source material such as the Player's Handbook. Effects are also checked when that same character is attacked, or damaged or has a saving throw, ability check or skill check forced on them (such as from a spell).

In other words effects are checked when a character attacks, does damage, makes a saving throw (including death saves) or makes an ability or skill check. In order for the effect to be properly executed the character must be on the Combat Tracker (CT) and either they or another actor must make a dice roll which involves the character. In Fantasy Grounds an effect is anything which gives the character either a bonus or penalty of some kind to a dice roll they are about to make. It is also, judging by the number of forum posts, the area where most users find the learning curve steepest. One of the most powerful features of the built in 5e ruleset is effects.

10.4 Specific PC Ability/Trait Examples.

8 Spells and Constitution Saving Throws.

Fantasy grounds 2 scripting