Sure. Of course, these are opinions so they might not be good game design. Here is one such example to encourage partying.
Most monsters gain an active skill that they use at most once upon being attacked by a player in a party. It allows them to call friends to aid them in the fight against the players. Essentially, it just summons more mobs.
- Summoned mobs cannot summon more mobs.
- Summoned mobs can be few or great in number, stronger or weaker compared to the summoner, of the same or different species as the summoner.
- There will be similarities lore-wise so friends of that monster will stay consistent. So for example Vubbes only summon other Vubbes. Jukopus summons red kepas and red kepas summon (at random) kepas, red kepas, and jukopus. Later on when you find palette swaps of jukopus, they summon similar friends, like a stronger red kepa.
- There are maps or sub area within maps that are better for solo or for party depending on their base exp and the base exp of the monster’s they summon. So alternate leveling spots depending on whether your class trains better at one or the other.
- Monsters can cast higher levels of the skill depending on the number of players in your party.
- Decent for controlling how many monsters are drawn at once to keep frame rate high. So instead of 10 mobs spawned at once. You spawn only 2 instead, but they each spawn 4 more. And you don’t have to fight both at once, unless you want to.
The more obvious way to encourage partying is to buff classes so that they have more party skills. Now went delving into game balance so this following suggestion may be more controversial than the last.
Say you have 2 sappers that want to party. They have no synergy with each other. Give them one. Sappers don’t need catalysts when near another sapper.
It doesn’t have to be class specific. Two wizards near each other could have halved cast time if the other isn’t also casting.
It can be cross class. A paladin near a thaumaturge gains bonus max hp and defense. This one is a little out in left field, I admit. I can’t think of any classes off the top of my head right now.