This is the same question as My prefix is weird, My suffix is a friend, but with a couple of ever-so-slight modifications (and obviously a different answer):
- My prefix is Weird.
- My suffix is a Friend.
- My infix is a creature to be feared.
- My whole has a massive extend*.
*Clarification (not needed, but may clear something up):
The verb 'extend' is being used as a noun here in order to fit the rhyme scheme. There isn't much more to it than that.