Ideas for events in survival map

[Ranger21]

I need some ideas for cool events which happens every n minutes.
I have this type of units for enemy:
Raptor (Walking Dragon)
Stalker (Small sneaky bug)
Pudge (no comments)
Flying Beast ( Some kind of violet bird)
Hi-Tech Skeleton (Skeleton with gun)
Alien Beast - (Small and sneaky fast-attacking zergling)

And this type of bosses:
UltraMega Raptor (Giant Raptor)
Nerubian (Some kind of assasin with blink)
Magheridon (Fat "tank" which able to knockback everything on his way)
Water Elemental (No comments)
Lava Elemental (No comments)
Lich (Shoot balls of ice and summon skeletons)
And something more bosses...

I need something to fit my map. Abilities, models, 2D art, events.

 

[gerf]

Elapsed 5 minutes in dragon nest (O_O) spawn n raptors. They run to center and attack all survivors. When raptors die, created Mego raptor, and when survivors kill him, he get n gold, and items.