I understand how rng works, or better  yet the idea of how it is suppose to work. Is it really random though? I ask because I popped 13 ancient crystals and received 4 spikeheads. I am not angry, if it wasnt spikehead it would have been other rares, I get it. But what are the odds of getting 4 spikes out of 13 pulls?

20% spikehead & 5% everything else is still RNG, just heavily shifted towards 1 hero. Since we don't know what the underlying probabilities are, Plarium can do what they want in the background.

Which they are already doing with those "double dwarves" or "doubled legendary chance" events.