Beezlemon is the champion of underdogs, saving you when you need it most.
He's best to use after losing a duel, then switching to impmon and digivolving to him. He's also great at defeating decks focused around Apokarimon. He also only requires two card slots (himself and Impmon) and can easily be splashed into any deck.
Combos with other cards:
Beezle Motorcycle gives him a gigantic attack boost, and sets him up for power-ups from several ability based option cards. Shining Digivolution and Ultra Digivolve will help you get him into play when you're in the lead.
Ways to counteract it:
Digivolve into a non-virus champion level digimon and use counter attack.
Beezlemon creates some very balancing interactions, and is overall very strong. I give him a 10/10.