That's cool, combo decks are much better at dealing with a lot of opponents. Commander damage type of decks can still get there in multiplayer, but they tend to do better with 7-ish attack power, low reliance on other cards, and a fair amount of control (i.e. Karrthus, Tyrant of Jund, Thraximundar, or Skithiryx, the Blight Dragon). Haste is always a plus.
Rafiq is a little less intimidating when people know you didn't build your strategy around him, but swinging for 8 each time will still force some much needed removal to target him. I had him in a five color deck where I managed to hit someone three times with him before they had removal. They were not happy.
As for the interesting cards since Khans of Tarkir:
Dragons of Tarkir Collected Company obviously this is a good card, but needs testing here to prove its usefulness since we only have roughly 22 creatures. Display of Dominance budget option for removal/counter to blue/black hate. Dromoka's Command could be decent depending on your meta. Epic Confrontation budget pump that can double as removal. Glaring Aegis budget pump that can get a blocker out of the way. Ojutai Exemplars slow, budget option to make all of your noncreature spells double as a way to tap down blockers, its a decent threat as a blocker if you suddenly give it first strike + lifelink, and if they try to remove it you can blink it with any noncreature spell. Ojutai's Command actually seems decent. It's versatile and it can potentially get you two infectors back from the graveyard.
Magic Origins Grasp of the Hieromancer budget option to repeatedly tap a blocker. Psychic Rebuttal could be useful in some cases to counter removal and/or turn it back on your opponent's creature. Send to Sleep budget option to tap down two blockers. Whirler Rogue budget option to repeatedly provide an unblockable buff.
Battle for Zendikar Swell of Growth the only decent card from this set that I could find for this type of deck.
Oath of the Gatewatch Reflector Mage decent option to get a problematic creature off the board for a couple of turns. Slip Through Space unblockable + cantrip for 1 mana. Void Grafter is a budget option for a way to counter a spell that targets one infect creature and provides you a 2/4 blocker.
Shadows over Innistrad Corrupted Grafstone budget acceleration, but needs something in the graveyard to work. Declaration in Stone solid removal, great against tokens. Eerie Interlude save your dudes. Ghostly Wings budget aura that pumps + flying and you can discard a card to return your infect creature to your hand. Gryff's Boon budget aura that pumps + flying and you can recur it from the graveyard. Haunted Cloak decent set of abilities to add to a creature, but no pumps. Open the Armory is a solid tutor that I'd strongly consider running in any Rafiq deck (infect or not). Rabid Bite again budget removal. Combined with a pump spell this can even help your infector get rid of an indestructible creature. Skeleton Key skulk is a decent effect, and it can help you ditch useless cards when the creature hits your opponent.
Rafiq is a little less intimidating when people know you didn't build your strategy around him, but swinging for 8 each time will still force some much needed removal to target him. I had him in a five color deck where I managed to hit someone three times with him before they had removal. They were not happy.
As for the interesting cards since Khans of Tarkir:
Fate Reforged
Monastery Siege maybe for a more controlling build?
Ruthless Instincts as a budget combat trick.
Valorous Stance as a budget removal or combat trick.
Dragons of Tarkir
Collected Company obviously this is a good card, but needs testing here to prove its usefulness since we only have roughly 22 creatures.
Display of Dominance budget option for removal/counter to blue/black hate.
Dromoka's Command could be decent depending on your meta.
Epic Confrontation budget pump that can double as removal.
Glaring Aegis budget pump that can get a blocker out of the way.
Ojutai Exemplars slow, budget option to make all of your noncreature spells double as a way to tap down blockers, its a decent threat as a blocker if you suddenly give it first strike + lifelink, and if they try to remove it you can blink it with any noncreature spell.
Ojutai's Command actually seems decent. It's versatile and it can potentially get you two infectors back from the graveyard.
Magic Origins
Grasp of the Hieromancer budget option to repeatedly tap a blocker.
Psychic Rebuttal could be useful in some cases to counter removal and/or turn it back on your opponent's creature.
Send to Sleep budget option to tap down two blockers.
Whirler Rogue budget option to repeatedly provide an unblockable buff.
Battle for Zendikar
Swell of Growth the only decent card from this set that I could find for this type of deck.
Oath of the Gatewatch
Reflector Mage decent option to get a problematic creature off the board for a couple of turns.
Slip Through Space unblockable + cantrip for 1 mana.
Void Grafter is a budget option for a way to counter a spell that targets one infect creature and provides you a 2/4 blocker.
Shadows over Innistrad
Corrupted Grafstone budget acceleration, but needs something in the graveyard to work.
Declaration in Stone solid removal, great against tokens.
Eerie Interlude save your dudes.
Ghostly Wings budget aura that pumps + flying and you can discard a card to return your infect creature to your hand.
Gryff's Boon budget aura that pumps + flying and you can recur it from the graveyard.
Haunted Cloak decent set of abilities to add to a creature, but no pumps.
Open the Armory is a solid tutor that I'd strongly consider running in any Rafiq deck (infect or not).
Rabid Bite again budget removal. Combined with a pump spell this can even help your infector get rid of an indestructible creature.
Skeleton Key skulk is a decent effect, and it can help you ditch useless cards when the creature hits your opponent.