Assassin, echo knight and Piercer

[KCWONDER99]

Hi all, my first post. I've had an idea rattling around in my head and was wondering if there was any chance I could get help in working out the first round damage of a character?

I was thinking of an echo knight 11/assasin 9 with maxed dex and a rapier. Feats needed would be piercer mainly and probably shadow touched to help get surprise rounds more consistently. Expertise in stealth and perception for sure.

In my head the combat starts with me getting suprise. Then using bonus action to set the echo I would use my 3 attacks ,all crits due to assassinate, 1 set of sneak attack, and one unleash incarnation, then action surge and 3 attacks and unleash incarnation again. Piercer adds another die per crit which is each attack and I can reroll once with it.

Is there any big error I am making in the build and how much damage could I churn out round one if I hit each time ?
*edit, forgot to mention dueling fighting style

[clash]

So long as you don't expect to get surprise frequently or you have talked to your dm and he will allow frequent surprise then I see no issues. I'd you haven't talked to your dm then just don't expect surprise very often, even with stealth expertise.

[Damon_Tor]

Gloomstalker 3 in place of three of your rogue levels would be great. Awesome stealth package including darkvision immunity, an initiative bonus which assassins need, and of course one extra attack with every attack action. Have your echo set before combat begins (consider using a bow for easier setup with stealth) and you can use your bonus action for Hunter's Mark instead.

[heavyfuel]

I agree that winning Initiative is key in this build, thus both levels in Ranger and the Alert feat are mandatory. I'd say Alert is higher priority than Piercer by quite a large margin.

Your first priority item-wise should be a Cloak of Elvenkind to make sure you never fail a Stealth check. I know a lot of people don't like to count on magic items, but it's only an uncommon item, so you should manage to track one down at some point and kill I mean buy from the owner

Also, you may wish to go elf or custom lineage to grab Elven Accuracy, as you really don't want to miss your alpha strike.

[KCWONDER99]

Perfect, thanks for the tips, all of them sound good

[heavyfuel]

Perfect, thanks for the tips, all of them sound good

If your DM allows the Revised Ranger (which they totally should as it's a far more well balanced class) then go for that. At 1st level you gain Advantage on Initiative checks

[Quietus]

Also, you may wish to go elf or custom lineage to grab Elven Accuracy, as you really don't want to miss your alpha strike.

RAW, Custom Lineage is not an Elf, and therefore does not qualify for Elven Accuracy. Consult your DM to see if Custom Lineage is right for you!