Masticore is good because first it is a 4/4 for 4 mana. That is a good deal
for an artifact creature. The 2 for regeneration makes it tough to get rid of,
which is something artifacts aren't known for. The 2 to do a point to
creatures give decks that shouldn't be able to deal with weenie creatures and
option. The fact that you must discard a card every turn is made up be the
fact that you can kill maybe 3 or 4 creatures while still beating your opponent
down 4 points a turn.
Morphling is one of the best creatures in the game due to its versatility. You
can make it flying to block a flyer or get some evasion. The untargettability
makes it hard to deal with. And the power/toughness abilities make it able to
win most creature encounters, or deal 5 points a turn. The untapping ability
makes it an easier choice of whether to attack or not. Morphling and Masticore
also allow you to play more lands in your deck without losing too much power
(which is a good thing)
If that doesn't help, just try playing with them. If you don't have any, try
some proxies. You'll understand after a few games.
-SSJ Goku
"Excuse me, has anyone seen my arm? You can't miss it, its green" -Raditz