RULE: Change ONLY one letter at a time and form a new word at each step.
#1 Change TEN to TWO. #2 Change TEN to SIX.
T E N T E N
T o N T I N
T O o S I N
T W o S I X
#3 Change FIVE to FOUR. #4 Change PIG to STY
F I V E P I G
F I l E w I G
F i l L w A G
f a l l w A Y
f a i l s A Y
F O I L S T Y
F O u L
F O U R
#5 Change TEN to ONE.
T E N
t i n a metal
t i p tilt
l i p edge
l i d cover
a i d help
a n d with ( a conjunction)
a n t insect
a c t perform
a c e a card
a r e a form of "to be"
o r e mineral
O N E
#6 Change MAD to DOG.
MAD
LAD
LAG
LOG
DOG
#7 Change LEAD to GOLD in four steps.
LEAD
MEAD
MELD
MOLD
GOLD
#8 Change TIME to WARP in four moves.
TIME
TAME
TARE
WARE
WARP
#9 Change GRASS to GREEN!
GRASS GRASS GRASS GRASS GRASS GRASS GRASS
CRASS GROSS GLASS TRASS BRASS GRABS CRASS
CRESS GROWS GLOSS TRESS BRANS CRABS CRAPS
TRESS GROWN FLOSS TREES BRAND CRIBS TRAPS
TREES GROIN FLOES TREEN BLAND CRIES TRIPS
FREES GROAN FLEES GREEN BLEND CRIER TRIES
FREED GROAT FREES BLEED CRIED TREES
GREED GREAT FREED BREED CREED TREED
GREEN GREET GREED GREED GREED GREED
GREEN GREEN GREEN GREEN GREEN
Martin Round sent in another solution:
GRASS CRASS CROSS CROPS DROPS DRIPS DRIES DRIED CRIED CREED GREED GREEN
#10 Change HEAD to TAIL.
HEAD HEAD HEAD HEAD
HEAL HEAL READ HEAL
SEAL TEAL REID HELL
SELL TELL RAID TELL
TELL TALL RAIL TALL
TALL TAIL TAIL TAIL
TAIL
#11 Change WINTER to SUMMER.
WINTER WINTER
WINNER WINDER
SINNER WANDER
SINNED WARDER
PINNED WARNER
PUNNED WARNED
PUNTED DARNED
PANTED DAMNED
PARTED DAMMED
DARTED HAMMED
DARNED HUMMED
DAMNED BUMMED
DAMMED SUMMED
DIMMED SUMMER
DIMMER
SIMMER
SUMMER
#12 Change STAR to WARS.
STAR STAR
SEAR SOAR
SEAS BOAR
TEAS BOAS
TENS BAAS
TANS BARS
TARS WARS
WARS
#13 Change BOY to MAN.
BOY BOY
TOY BAY
TON MAY
TAN MAN
MAN
#14 Change WOOD to FIRE.
WOOD
FOOD
FORD
FORE
FIRE
#15 Change ARM to LEG.
ARM
AIM
AIR
FIR
FIG
BIG
BEG
LEG
#16 Change HAND TO FEET.
HAND
SAND
SEND
SEED
FEED
FEET