Eclipse adds to the creature's base attack, but doesn't change the base attack itself. Burrow, on the other hand, actually changes the creature's base attack. If you burrow a Pest with an Eclipse out, the burrow halves the base attack, not the 2 attack. So there is no way you can abuse any kind of weird timing loopholes by doing a burrow/Eclipse/unburrow trick to try to get a 4 damage Pest.
Antimatter takes the current attack, multiplies it by -1, and assigns that number to be the new base attack. So when your Pest becomes antimattered, its new base attack is -2, not zero. But when Eclipse is removed, your Pest loses another 2 attack, because the initial gain of 2 was lost due to antimatter.
So, to answer my question, when you have these -4/4 creatures like
Tea is good had at the time, then you burrow them, they would remain at -4/4. And Eclipse would bring them back to -2/5 regardless if they're burrowed or not. That makes sense, thanks.
EDIT: Ok, just tried it in the trainer because I'm crazy like that. And the results were a little different than what I had predicted.
The -4/4 Pest became -2/4 when burrowed. Adding Eclipse (while burrowed) made it 0/5. Unburrowing it made it -2/5.
Antimattering the -4/4 Pest became 4/4. Adding Eclipse made it 6/5. Burrowing this made it 4/5.
Antimattering the 6/5 made it -6/5. Exploding the Eclipse made it -8/4. Burrowing this made it -4/4.
So you can keep on adding 4 attack to a death or darkness creature by playing Eclipse, using Antimatter, destroying Eclipse and then using Antimatter again. Not that you'd want to, but you could.