Secondary skills in Heroes 3.

The cost of upgrading a manticore to a scorpius, in my opinion, is 100 or 300 gold. It's not a big deal. And there's no need to criticize diplomacy. Whether or not to take the skill depends on the situation, i.e., how many and what kind of neutral creatures are scattered on the map, their quantity, etc. Only after considering all this, you have the right to choose whether to take the skill or not. No matter how you look at it, I think intelligence is rarely a useful skill. If you're focusing on magic, take a mage; their knowledge and spellcasting skills are immediately improved. If you're focusing on a warrior, take attack.