No, casting a creature spell does not allow you to draw a card.
No, you do not draw a card when a creature dies.
When you activate the ability "draw a card for each creature you control," you draw a number of cards equal to the total number of creatures you control.
Mulldrifter is a creature with an enters-the-battlefield effect that allows you to draw a card when it enters the battlefield.
Mutation cards are extremely rare, so rare you can only find them in the bazaar. Buy one and get the required spell it can mutate trained. When you are in combat with the mutatable spell in your hand, discard a card you don't need and/or want by right clicking them, then click the Draw button at the bottom to draw the mutation card (if you have other treasure cards included, you might not draw the right one as it randomly chooses). When you draw the mutation spell, just click on it, then the mutatable spell you have in hand and it will turn it into a mutated treasure card in which you can use.
I suppose the seraph treasure card you got on Unicorn Way? Well it's plainly simple, just go to your spell deck, click on the treasure card tab, and click on the seraph treasure card. Then, in battle, discard one card by right-clicking it, then click the draw button. If you have enough pips and mana, you can cast it.
No, you cannot put a Draw 4 card on top of a Draw 2 card in Uno.
No, you cannot put a Draw 2 card on top of a Draw 4 card in Uno.
No, you cannot put a Draw 4 card on top of a Draw 2 card in Uno.
No, you cannot stack a Draw 2 card on top of a Draw 4 card in Uno.
No, you cannot stack a Draw 4 card on top of a Draw 2 card in Uno.
No, you cannot put down a Draw 4 card on top of a Draw 2 card in the game.
No, you cannot stack a Draw 4 card on top of a Draw 2 card in the game of Uno.