In combination with divides and the 2x spell, this spell can be used to make far more copies of other spells than is normally possible.
What DRAW_EAT Does & Relation to Wrapping
DRAW_EAT is very simple. When it’s drawn into the hand, it discards itself. This doesn’t do anything much on its own; the only thing it accomplishes is to eat a single draw, much as its name implies. This is remarkable because it allows a draw to be resolved without increasing the number of spells in the hand. This is only normally possible via OOC / OOM (Out Of Charges / Out Of Mana) spells when they are drawn as the last spell in the Deck. However, for this build it is required to have that functionality work in the middle of the Deck.
And that’s a problem, because in order to wrap a wand, draw is necessary. Specifically, a wrap happens when the deck is empty and you try to draw. But when this happens, the draw must then go on to cast one of the new spells in the deck, adding it to the hand. There’s no good way around it: if you want to wrap in vanilla, the price is that you increase the hand size by at least one.
This places a hard limit on the number of wraps a wand can do, since hand size can never decrease and you only get 26 spells (wand refresh can empty the hand, but it itself disables further wrapping and can only be cast once anyway). There is a mechanic using Wand Refresh and AC (Always Cast) that allows one to dupe the AC spell and add more of them into the Deck but it is too complicated to work around.
So this is the background for DRAW_EAT
It’s a very limited way to decrease hand size (it can discard itself from the hand) and this allows for a wrap to be executed without paying the price of permanently increasing the hand size. As a result, there is no limit on the number of wraps that can be executed on a wand with DRAW_EAT. In fact, some of the wands we will see below will wrap in excess of 10,000 times on a single cast. As one might expect, this allows for some big numbers!
Aside
It actually isn’t strictly impossible in vanilla to wrap without increasing hand size, it’s just the the only way to do it is useless. You do it by having the deck full of uncastable spells. If a spell is uncastable (either 0-charge or not enough mana), then the draw will look at it, decide it can’t be cast, and then send it into the discard before looking to the next spell in the deck.
If you wrap, but everything in the deck is uncastable, then the draw will discard everything and eventually arrive at the end of the deck before giving up. It won’t increase the hand size. So it is technically possible in vanilla, it’s just that doing it like this will leave you with an empty deck, which defeats the purpose of wrapping at all.