If a picture is worth a thousand words, here you go.
For the record, that would be my librarian HQ being attacked by fifteen termagaunts, one from a regular troop unit and the rest spawned by a monstrous creature (lurking at the top up there). The Tyranids' ally, the Tau, are ready to hose him with blasters should he somehow manage to kill all of them.
This was after the first turn, where upon going first I tried to have the librarian cast Warp Gate (or whatever it is), roll two ones on the Psychic Test, take a wound, and then roll doubles on the scatter and kill a member of his accompanying unit. Then in the shooting phase my plasma cannon-wielding marine lit himself on fire with his weapon, meaning I've given myself three wounds before my opponents have even gone.
The one good part? On the previous game that evening, also against the Tyranid opponent, my librarian rammed his Force Weapon into one of his monstrous creature's necks and flicked on the juice. First time the guy had seen a librarian in action, and he wasn't pleased. Thus in game two, he swamped the librarian and his unit with 'gaunts.
To his credit, the librarian actually held out three turns before succumbing to the onslaught. He scythed his way through a good dozen of them, though. He might get fully painted soon as a result.