It's important to see that alliances are always opportunistic and temporary based on your org current tactical objectives. An alliance that makes your org subservient to a liberal org or to a broader alliance can be dangerous as it will end up making the communists irrelevant. Not to mention the numerous cases of betrayal in our history.

It's not about the greater ideological evil, it's about recognizing what is the primary contradiction and the greatest current impediment to your goals. You can be ideologically closer to faction X than to faction Y, but if faction X is the bigger obstacle right now to advancing the socialist cause then it is X you should be focusing on fighting, not Y.

I mean that's essentially what China is doing in allying with Russia and Iran. It's what the early communists in China did in conditionally allying with the KMT against imperialist invaders (but they eventually had to confront them and defeat them).

It can easily get silly though when we're talking about communists participating in bourgeois elections by allying with bourgeoisie parties. Although a case like Brazilian comrades trying to keep Lula over a Bolsonaro may be in its way a move to keep the worst of imperialist comprador control out, a case like Yankee communists voting for democrats can quickly get absurd, where it's essentially just communists demanding nothing for their vote and falling to blackmail that "it will get worse if they don't."

In other words, I'd say a rough litmus test is that there is some kind of strategic gain from it, especially as longer-term strategy. Hell, write a basic pros and cons list if it crystallizes things better. Get it out of the abstract and into what the real consequences are.

A lot of people here bring up China and Russia as an example, and while they have good relations and presently aligned interests, I think many of us here are overstating the level of commitment in this relationship. "Allying" is a very strong word to describe China's partnerships with Russia and especially with Iran, a more fitting example would be the DPRK and it's cooperation with Russia, which is a lot closer to an Alliance than China's more "soft" strategic partnership.

There is no binding bilateral security agreement between Russia and China, no formal mutual defense pact etc.

Whereas the DPRK and Russia definitely do have this

https://en.wikipedia.org/wiki/North_Korean%E2%80%93Russian_Treaty_on_Comprehensive_Strategic_Partnership

They already do, this is the nature of both multipolarity and anti-imperialism. China continues works with Russia. China also works with the Global South including groups like the Axis of Resistance.

Tactically yes. We can always align with others (Usually nationalists from the periphery) on our immediate common goals. Strategically no. In every single example across the history of revolutionary movements the non-marxist element of every united front will betray the marxists as soon as they believe we are no longer a useful ally in the struggle. The only way to prevent this is to subjugate these other groups under a Proletarian Dictatorship. See China for an example of both what to do and what not to do.

It always depends on the context but yeah.

i mean, even marx and lenin promoted that thing (but never forgetting that we shouldn't trust too much in them, because they tend to betray the proletariat with great frequency)

Yes, absolutely

Depends.

Is this a proverbial fight as in just general struggle/agitation? Probably not.

If it's a literal, violent fight where lives are on the line then having reliable support is a net positive no matter who it's from.