What could go wrong with a North Korean Hydrogen bomb test over the pacific Ocean?

If this is an ICBM with a miniature Hydrogen bomb attached to the nose cone somehow, the first problem is at the launch site where the Hydrogen bomb could go off ending North Korea itself (depending how many megatons of hydrogen bomb this is on the tip of the ICBM).

2nd, it could go off soon after takeoff rendering parts of North Korea, South Korea, China, Japan etc. uninhabitable for hundreds of years just like Fukushima has rendered that area uninhabitable for likely at least the rest of this century or longer because of nuclear meltdowns.

Third the booster could fail and the bomb go off underwater which likely could cause both a 9.0 or bigger earthquake if it was resting on the bottom of the ocean,

Or it could go off within 30 feet of the surface and cause 1000 foot tidal waves wiping out all cities eventually under 1000 feet in elevation everywhere on the Pacific Ocean and completely submerging islands and killing all people that are under 1000 feet in elevation.

And this is just what an  ICBM failure looks like. This is just if the test fails. Imagine if it was a success?