

Doctor Doom is probably Taskmaster's single best friend, and you will generally never be wrong putting him behind Tony Masters in either 2nd or Anchor position. Doctor Doom is a capable damage engine via TAC or DHC, and Taskmaster can use all three of Doctor Doom's assists extremely well. Plasma Beam is useful for full-screen coverage and late-combo extensions, as well as giving Taskmaster the ability to convert off his air back throw. Those same extensions can come off Molecular Shield, which also enables Task to convert off his front grounded and air throws, and give him a slow, meaty assist to cover an approach. Finally, Hidden Missiles can help him fight airborne characters like Magneto or M.O.D.O.K. who desire to hang out in the corner and zone you. Additionally, Missiles enables Taskmaster to do unique combo extensions that pump his already impressive damage into the stratosphere. All three assists enable unblockables with good timing, though in terms of ease it goes Missiles > Shield > Beam. However, none compare to the ease of use of Taskmaster's other best friend, Dante.
Dante is the 2nd best support character in the game, and this is just as true for Taskmaster. Jam Session is the unblockable-enabling assist. If building your strategy around unblockables, pick Dante. A simple Jam Session call to lock the opponent down and keep them from pushblocking away enables Taskmaster to easily land a (blocked) L Sword Master (623L) and follow up with an H headbutt. From there, he can follow up with either Lights Out (236H) if in the corner and with appropriate assists, or with X-factor to secure the kill. This is all in addition Jam's fantastic defensive utility, which can and will bail you out when the opponent is rushing in while it secures you hits when you have them backed into the corner. S+ tier assist, and Taskmaster makes great use of it. Devil Trigger is a safe DHC, and Million Dollars is an excellent bit of cleanup to kill anyone who isn't finished off by your looped supers. Finally, Dante's TAC infinite allows for Timer-Scam strategies, which can be very powerful on a team with a bulky point who can either bully or zone as required.
Vergil is the best or 2nd-best Damage Engine in the game and his utility for Taskmaster in particular is surprisingly strong. Taskmaster can protect Rapid Slash even full screen by using his arrows (236X) or Legion Arrow (236XX), and Rapid Slash enables certain extremely damaging combo extensions which can then lead flawlessly into Spiral Sword loops, netting one-touch kills on the entire cast without the need for a TAC. Vergil is very meter-hungry and Taskmaster can be an able battery for him with his 1.1 million hp and ample chip damage. Spiral Swords and Devil Trigger are both safe DHCs off either Legion Arrow or Aegis Counter, and Vergil can even use Taskmaster's arrows to do teleport shenanigans. Amazing pair.
Spencer is a uniquely utilitarian pick for Taskmaster. His ability as a damage engine and strong mid rivals that of Vergil, though his anchor capabilities pale a bit before the Son of Sparda. Spencer's Slant Shot assist restands the opponent, allowing for certain powerful extensions, such as following up after Lights Out after an unblockable, or following up after his Front Throws. Spencer's ability to loop Bionic Maneuvers hypers combined with Taskmaster's complete lack of Wallbounces means that he can secure a kill against the whole cast off a single hit. What's more, Spencer actually quite likes having Taskmaster 2nd, being able to utilize Taskmaster's lateral arrows assist in his incoming mixups and to get an additional up-grapple off a team hyper combo juggle into a full combo. Taskmaster and Spencer have uniquely strong two-way synergy and the pair is absolutely worth your time.
Dormammu is an excellent 2nd behind Taskmaster on point, the pair covering for one another's weaknesses splendidly. Taskmaster serves as a superior point character with his ability to hang with the faster rushdown who would maul Dormammu at 99. He also serves as a battery, chipping the opponent down or even securing kills while accruing meter which Dormammu can then use to cash out for either Chaotic Flame or Stalking Flare, two of the highest-return hypers in the entire game. Chaotic Flame as a DHC after Legion Arrow secures many kills which other hypers would fail to manage, and Stalking Flare is an unconventional - but effective - way to set up Taskmaster's unblockable - though it is surprisingly difficult on incoming. Furthermore, Dormammu quite likes either taskmaster's up arrows or (more commonly) lateral arrows assists. Finally, Taskmaster is one of the best characters in the game at using Dark Hole, being able to use it both for late-combo extensions and also for easy unblockable setups in neutral or on incoming.

Everything Doctor Doom does for Taskmaster, Iron Man can also do - if he has to work a bit harder to get there. Iron Man serves as a damage engine off DHC or TAC, as well as his Unibeam assist doing many of the same things that Plasma Beam does, and being slightly better for random unblockables.
Sentinel Drones is another excellent choice for Taskmaster, giving him a slow meaty assist to dash in after and an outstanding vehicle to deliver unblockables. Ronan Healy has proven the effectiveness of Taskmaster with drones. Taskmaster can protect Sentinel fairly well between Shield Skills and his various Arrow specials and hypers, and Sentinel provides decent DHC synergy to Taskmaster as well, with Plasma Storm in particular being a good cleanup hyper if Sentinel is on 2nd.
Littlest but certainly not least, Dagger Toss assist is incredibly powerful with Taskmaster, especially when empowered with King's Armor. Placing Arthur 2nd at round start enables Taskmaster to act as a battery, build up to 2 meters, and then safely DHC into King's Armor before immediately dry tagging back in, now with perhaps the best lateral coverage assist in the game. Dagger Toss enables Taskmaster to convert off full-screen arrows (236L) by plinking up 3-4 times and linking with Charging Star into a full combo. Combined with his 9 points of projectile durability from a fully charged arrows, Arthur's dagger toss either doubles it (unpowered) to 18 points or nearly triples it (empowered) to 24. All in all, the pair works quite well together, and what King doesn't have a few mercenaries under his command?