One potential feature that could allow skillers to fight bosses using their skills is to introduce unique boss mechanics that require players to use their non-combat skills in order to defeat the boss. Here are a few examples:
Mining boss: This boss could have a thick layer of armor that must be mined away before it can take damage from weapons. Players would need to have a high enough mining level to be able to chip away at the boss's armor, and perhaps different types of pickaxes could be required to mine different types of armor.
Fishing boss: This boss could be fought by luring it onto land using various fishing techniques. For example, players might need to use their fishing skill to catch bait that can be used to lure the boss onto a specific spot, or they might need to use their cooking skill to prepare a special dish that will attract the boss.
To further incentivize players to engage with these skill-based boss fights, it could be added that the bosses drop items that provide advantages to those skillers. These items could increase the amount of resources harvested or increase the speed of harvesting, for example. To create competitiveness, these boss drop items should be extremely rare and only obtainable via the respective skilling function of the boss. Furthermore, these items should be untradeable and have a tax to unlock them (e.g. 5 million coins) to make them truly unique rewards. To further encourage players to engage with these bosses, there could be multiple tiers of bosses for each respective skill, each dropping a unique item, leading to a collecting element to these rewards.
Overall, the key to making skill-based boss fights work is to create mechanics that are both challenging and rewarding for players with high skill levels in non-combat skills. By doing so, skillers can feel like they have a meaningful role to play in boss fights, while still being able to use their preferred skills to contribute to the battle.