I have been running Dungeon and Dragons 5e since it came out. Overall I enjoy it and think its an excellent product. It is a highly refined version of 3.5e that also manages to evoke the feel of older editions like 1e.
However, the problem with many of the monsters is they tend to be pretty boring and run very samey due to generic abilities. From little things like every creature having multiattack instead of something a bit more evocative like “Snake Eyes. The medusa attacks twice with her snake hair” to having terrible action economy and being murdered outright by parties. The biggest issue is with spellcasting monsters. They are time-consuming to run for the DM (I need to either know all those spells or have them handy in some manner) and for that preparation, they tend to be paper tigers collapsing while still buffing themselves during round 2 of combat.
Not worth the effort.
Reaching back to 4e monster design I started converting monsters as I needed for my own game to make them easier to and more fun to run for myself. Essentially the general philosophy I follow is to make unique monsters as needed with specific abilities. I will start posting some examples of conversions over the next few weeks (or as I make them). But first action economy.
5e Monster Action Economy
Once characters leave level one they should be able to trounce single/solo monsters many CRs above their level mainly due to the action economy – they get way more actions against monsters. Legendary and Lair Actions can help here – and that’s the idea – but I know as a DM I forget them a lot during actual play. I ended up giving monsters multiple initiative counts. I would do this by ear for non-epic monsters. Whenever I wanted a monster to be a signficant threat I would give the monster two initiative counts. That is, it would have two full actions each round. My rule of thumb was 1 initiative count per 4 players. Once players are higher than level 10 reduce that ratio to 3 to 1. This is much easier to run and remember than reaction type moves based on character turns (like Legendary Actions).
For actual Legendary creatures, like dragons, I would add 1 initiative count for the dragon proper, 1 initiative count for lair actions and 1 initiative per Legendary action. If I thought I needed to add more counts I would add them to the dragon proper. This dragon is an actual challenge for characters of the same level.
Finally, I use reactions a lot. Sometimes having multiple options – for example when the creature is bloodied (at 50% hit-points or less) and when the creature suffers some kind of attack.
And now here is the lich one of the worst offenders – lots of spells, rubbish hit-points and a paucity of actions for all those spells.
Medium undead, any evil alignment
Armor Class 19 (natural armor, mage armour)
Saving Throws Con +10, Int +12, Wis +9
Legendary Resistance (3/Day): If the lich fails a saving throw, it can choose to succeed instead.
Rejuvenation. If it has a phylactery, a destroyed lich gains a new body in 1d10 days, regaining all its hit points and becoming active again. The new body appears within 5 feet of the phylactery.
Turn Resistance. The lich has advantage on saving throws against any effect that turns undead.
Shadow Ray. Ranged Spell Attack: +12 to hit, reach 100 ft., one creature.
Hit: 16 (4d8) necrotic damage.
Necrotic Orb. Ranged Spell Attack: +12 to hit, reach 100 ft., one creature.
Hit: 12 (3d8) necrotic damage, and the target is stunned until the end of the lich’s next turn.
Frightening Gaze. When the lich is struck by a melee or ranged attack it may fix its gaze on one creature it can see within 30 feet of it. The target must succeed on a DC 18 Wisdom saving throw against this magic or become frightened for 1 minute. The frightened target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a target’s saving throw is successful or the effect ends for it, the target is immune to the lich’s gaze for the next 24 hours.
A lich is a gaunt, skeletal humanoid with withered skin stretched tightly across its bones. Its eyes have been lost to decay, but bright pinpoints of evil light burn in the empty sockets. A lich usually dresses in the rich robes and vestments it wore in life, although with the passing of the years these usually fade into tattered remnants.