Trippled HP on a poorly played Lich will only postpone the battle by 300%
This does not equate to 5E encounter building by the book is broken!
How about we erase all of the discussion using the monty haul PC's, which were being touted as the encounter munching party referenced by Celtavian, until he proudly proclaimed we just look at the character sheets when questioned on the topic, and after which when we all were left jaws agape, proclaimed that that was a bad example...
wasn't it they that was his original example?
such circumlocution!
likewise, a poorly played Lich encounter, by the DMs own admission a bad example, yet had been used as AN example...
let's erase that from the conversation as well...
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Now from my experience, if you have more than 4 or 5 experienced players, the Encounter builder will come off to easy at first. But once the 5E system was dialed in for me, I have little trouble DMing in the same fashion I DM'd 1E and 2E and keeping my group on their toes. But I am an experienced DM, as it would seem are most everyone else posting here; so you all should know that the rules are your guidelines and toolkit, that the idea of building an encounter without fleshing it out and adding factors to create an environment and challenge on par to the gaming level of your players is, well, it isn't good DMing.
Furthermore, I feel that a group of people playing D&D for the first time would not find it as easy, in fact the system would work as intended.