Base designs:
I personally like DeRouen's base. It's worked well for me through
HBM S. I know other people like War-Machine's base or
Hyuga16's base as well. Hyuga is a side base, and DeRouen and
WM are corner bases.
In HBM S, and also T, the giant Molt can kill your buildings if
he procs in the right direction. I'm not sure if it's possible to
level up your buildings that are inside your walls so they're
strong enough to survive this, but I know that luck plays a
significant part in passing S. The direction the spawns come
from can determine if you have no chance, or if you will have
a shot at taking down all the monsters.
The heroes that you use will also matter, of course, as well as
their placement within your base. PD and VD are necessities.
Some people leave out Cupid since his proc is rarely in sync
with the energy levels of your other heroes to make a big
difference, although the dmg buff can be nice. You also need
a healer or 2... GLM and/or Dru... GLM is better b/c of the
AOE dmg and dmg reduction, but Dru's dmg buff with no CD
can also be nice.
There are several ways to kill the giant Molt. Debuffers
(atk speed, atk dmg, and/or move speed, such as Molt/HQ),
heroes with high scatter to keep it from proccing, or pure DPS
(Succubus can be used here b/c the giant Molt has no dmg
cap in HBM S and T, although it can be tricky to keep her
alive until the last wave). Other AOE heroes can also be
very useful, such as SB and IMMO. SK can be used as
well b/c of his survivability and high dmg. Don't use heroes
like WL or DD. Having evolved heroes really helps b/c of their
increased HP and dmg.
Place ranged heroes, preferably flying ranged heroes, closest
to the fattest part of your walls, so they won't jump out and
get killed. Place PD in the very center since he's really
important. I place healers towards the back.
All your heroes that don't have Revive as a main talent
should have revive crests. Also use the appropriate
Artifacts on your heroes, to help them survive longer or
dish out more dmg.
As with most other challenges in the game, it's important to
observe what happens, so you can see where your weak
points are, and how you can change things in future runs.
Also, as mentioned before, luck does play a part in your
success, so keep trying and making adjustments until
you succeed. If you don't come that close to succeeding,
i suggest trying less often so you don't waste all your
turns for that tiny chance of success. Your odds will
improve as your heroes and buildings get stronger, but
you need to keep feeding your heroes with HBM R, or
whichever level you're able to sweep.