Witch Doctor

Pros:

Guaranteed net damage disregarding bypass tricks or AI breakers

requires only 1-2 credits to use, 1 net damage could mean the differences between a painful Snare! and a deadly one.

Synergy with other psi and AP cards like Hyoubu Research Facility, Upayoga, Nisei Division: The Next Generation, and Synth DNA Modification

Cons:

Can be trivially broken by most AI

Small effect might not be meaningful enough for jinteki decks

Overall a replacement for the now rotated Data Mine, might be worth a look in some AgInfusion: New Miracles for a New World or Jinteki: Potential Unleashed decks.

I see some use for this in a Chronos Protocol deck, provided you draw it early enough. If you draw it early it has a good potential to snipe a key card from the runner's hand, even if you're otherwise low on credits. Later in the game the effect will be smaller as the runner will mostly have set up their tools and the chance of an AI being out is higher.

A more subtle use of Mganga can be to trick the user into getting their AI breaker on the board and then using cards that are worse when there's an AI breaker such as Chiyashi. However, this is something which works with other traps such as Whirlpool as well and I'd rate Whirlpool higher in terms of scariness (with Mganga you know what you could get, with Whirlpool there's the potential of running into some deep nasty traps with no way out). On the other hand Mganga is reliable, it doesn't need a server with ice behind it and/or facedown cards inside it to be scary.

• Problem: everything that Mganga does, there are better alternatives which last longer and create more value over time. Hokusai Grid costs you 0-1 more and is only trashed if the runner pays $4. It might even be cheaper if Mganga has an install cost. (God, I hope you're not installing Mganga alone). Hokusai Grid also doesn't get trashed on Stargate runs. Among ice, I'd recommend looking at Aiki, Anansi, Saisentan, and (Startup only) Engram Flush first.
• If your main goal is milling the runner, even Aimor is also more effective than Mganga.
• The only situation where I'd rather have Mganga than Aiki is in protecting Obokata. 1-2 reliable net damage may save Obokata. But it'd be a nightmare situation where I'd rather have Mganga than Hokusai. Consider all of the things that need to be true (Hokusai's reliable 1 net damage is no good, I NEED 2 net damage right now, and I have enough money to max out the psi game, and the runner does not have Engolo/AI to break Mganga). Stick with Hokusai, it's so much better in every other situation.
• Generally used in hyper-mill setups with heavy recursion. If you are FULLY committed to heavy recursion, it's easier to use extra copies of Mganga than extra copies of Hokusai.