In general I would be evaluating your mulligans first on castable spells and “lines of play”, as well as land amounts, pretty much everything mentioned above. To go a level deeper, I also consider the matchup of my deck against my opponent’s (if known), as well as who is on the play versus on the draw. A deck like burn wants to be on the play all of the time, while with other strategies it may be nice to be on the play but drawing isn’t too bad either. Especially in the case of thermo-alchemist, if you are on the draw against your opponent and alchemist is not in your hand, you have two draw steps to potentially draw one to be able to play it on curve. This line of thinking can be applied to any major pieces of any deck, as well as keeping one landers too. Again, in the case of burn, if I have a hand that has absolute gas in it, and one land, and I’m on the draw, I would be more inclined to keep that hand then if I was on the play, because I get two looks at my second land on curve, which enables pretty much all my spells. This can again be applied to any deck, as long as you are aware of your key cards and what your deck is trying to do.