A Foundry VTT module for DMs that want to add tokens to ongoing combat more smoothly.
JoinCombat.mov
With the Join Combat button toggled, dropped tokens will automatically join combat and roll their initiative. This functionality is system agnostic and should work for all systems.
For supported systems there is an additional button that can be toggled, Join Same Round. When this is toggled, dropped tokens will always end up at a lower initiative than the current combatant. Usefull for when the creature is meant to be able to act in the same combat round. Supported systems for this feature are currently: dnd5e