Random Puzzles 

Workings

Hint
This is a well known nursery rhyme.

Answer
HDD.

The initial letters from the nursery rhyme, Hickory Dickory Dock.
Hickory, dickory, dock,
The mouse ran up the clock,
The clock struck one,
The mouse ran down,
Hickory, dickory, dock.

Workings

Hint
This thing isn't alive.

Answer
A bed.

Workings

Hint
Think about it carefully.

Answer
A hole, or a shadow.

Workings

Hint
Another example, PEN is a complete word because:
   -en = ten
   p-n = pin
   pe- = pea

Answer
Three of the words are not complete: flew, rook, lamp.

Reasoning
The remaining 7 words can be changed as follows:
team:  -eam = beam
 t-am = tram
 te-m = term
 tea- = tear

cost:  -ost = host
 c-st = cast
 co-t = coat
 cos- = cosy

flew:  -lew = blew
 f-ew = ---- X
 fl-w = flow
 fle- = flex

ward:  -ard = card
 w-rd = word
 wa-d = wand
 war- = warm

fail:  -ail = nail
 f-il = foil
 fa-l = fall
 fai- = fair

rook:  -ook = book
 r-ok = ---- X
 ro-k = rock
 roo- = roof

soft:  -oft = loft
 s-ft = sift
 so-t = sort
 sof- = sofa

most:  -ost = cost
 m-st = mast
 mo-t = moat
 mos- = moss

lamp:  -amp = damp
 l-mp = lump
 la-p = ---- X
 lam- = lamb
Note that LARP is an uppercase acronym, and not in any of my word lists.

load:  -oad = road
 l-ad = lead
 lo-d = loud
 loa- = loaf