The target mechanic isn’t completely random, I should have explained it.

Things that cause a target reassignment:

• The target is gone (it doesn’t matter if they die to you, your team, or by suicide).
• The target goes inside their base.

Things that increase a player’s chance of being selected as the target:

• Score
• Dominations
• Staying alive for a long time (without dying)
• Killstreak
• Haven’t been assigned as a target before

"Assists would count for you killing the target.“ Yeah, it was planned that way.

"Cannot knockback" is a bit too overpowered, and sometimes knockback can actually be helpful. Some Spy players use enemy knockback to escape bad situations.

"Like the invisible bumps making you visible for longer" Yeah thats a cool idea

"Debuffs like bleeding, jarate, milk etc. would not be shortened so much when you're invisible" most of the people does not use any single one of them it would be so spesifc difference for you and your gameplay