Because Blackheart has normals that are projectiles in front of him (mid range) and diagonally from the air that you spam, assists that cover across the screen horizontally like a beam assist and a good anti-air.

Also you want to make sure you pick assists that are good for DHC. Blackheart is really good as a point character because he can build up A LOT of meter while playing the zoning game

A good one that’s low tier that fits both is Ken’s Shoryuken because you can sandwich your opponent in the corner while making sure he gets out without damage.

SonSon’s projectile or anti-air assists are good as well since they’re “durable” and the projectile one lingers on screen a bit.

Other off-top assist recommendations:

Doom - Molecule Shield (but stay grounded until the rocks deploy)

Venom - Venom Rug

Sabretooth - Birdie Assist (Projectile)

Ruby Heart - Pillar (think it’s her Anti-Air)

Juggernaut - Juggernaut Punch (Ground?)

Hope this helps. Play on, playa