CapnZapp
Legend
The by far easiest solution is to browse Appendix B of the Monster Manual and simply pick the nearest equivalent NPC.
A necromancer of about level 12? Take the Mage NPC, give him 3d8 extra hp (total 53), and a sixth level spell slot. Then select "necromanty" spells from the PHB, using his AD&D spell selection as inspiration. Done.
Assassins of level 3 won't actually be assassins (yet), just ordinary thugs. The Spy NPC is a ready-made stat block with the crucial sneak attack ability you need, so you could use that. You could use the Thug NPC if you want to fill out the encounter with fodder (if the heroes are supposed to be outnumbered 1 to 3, for example, or if their level is on the low side).
Manufacturing new statblocks is for the most party way too much work for a game like 5th edition.
In fact, spending hours to create NPCs that die in seconds is the singular reason I quit 3rd edition, so there is that.
A necromancer of about level 12? Take the Mage NPC, give him 3d8 extra hp (total 53), and a sixth level spell slot. Then select "necromanty" spells from the PHB, using his AD&D spell selection as inspiration. Done.
Assassins of level 3 won't actually be assassins (yet), just ordinary thugs. The Spy NPC is a ready-made stat block with the crucial sneak attack ability you need, so you could use that. You could use the Thug NPC if you want to fill out the encounter with fodder (if the heroes are supposed to be outnumbered 1 to 3, for example, or if their level is on the low side).
Manufacturing new statblocks is for the most party way too much work for a game like 5th edition.
In fact, spending hours to create NPCs that die in seconds is the singular reason I quit 3rd edition, so there is that.
