I have a couple.
How about dugtrio?
you never know what is under the ground for them, and they have a weird movepool.
Breloom, like said before, a fighting mushroom.
its based off of a kangaroo because of its shape and boxing ability, but it just seems like it always a trick under its sleeve.
Abamasnow, hmm.
Its supposedly an abominable snowman, but its just a frozen tree. Strange indeed.
and weezing.
I have never found out what it is, but i always thought of it as a faced poison cloud.
I just think every strange pokémon is interesting.