How to handle dual initiative mythic ability

I'm seeking suggestions on how to run a mythic creature with the dual initiative feat in FG with the combat tracker.

Dual Initiative (Ex)

The monster gets two turns each round, one on its initiative count and another on its initiative count – 20. For example, if the monster's initiative is 23, for its first turn it could make a full attack (and take a 5 foot step) at initiative 23, and for its second turn at initiative 3 it could take a move action and cast a spell. This allows the monster to perform two actions per round that normally take an entire round, such as using a summon monster spell. For the purposes of spells and effects that have a duration of a round or longer or trigger at the beginning of the creature's round or the start of its turn such as saving throws against ongoing effects or taking bleed damage), only the monster's first turn each round counts toward such durations.

Format: +21/+1; Location: Initiative.

I'm thinking about just putting a dummy NPC at the second initiative, but I'm wondering if anything screwy will happen because it isn't the turn of the NPC actually doing the attacking. And also, because the second dummy NPC won't be on the map.

Thoughts?

I guess the other thing I could do is just manually adjust it's initiative after it's turn. That's what I'll probably do, that doesn't sound too bad.

I'd say make a place holder in the CT for the second initiative slot. Keep the first init slot as the main one with links to the token/NPC statblock.

There's no issue with "the second dummy NPC won't be on the map" as it isn't a second NPC - it's the same one. There may be a little confusion with the players wondering who is acting - so use the same name with a reference added at the beginning or end of the name.

If effects come into play on the init of the second slot then just make sure the effect entry has the second init value recorded.

Make sure for targeting that the NPC token is selected (left-click) first.

Other than that you should be fine - it's really no different from doing something like an attack of opportunity. The main thing to keep proper track of is the init value for any effects applying to the main NPC record being added on the second init slot.