I don't care how strong it is; if it needs to take a multiple of six turns and at least two to three more cards to be strong, even if it's serving as a wall in the meantime, it's UP by the law of Reverse Time.
EDIT: Going by the "average 3 attack per creature", since Basilisk Blood gives +20 HP and 6 turns delay, you'd be worse off by playing BB unless your opponent has only one creature out (more accurately, less than 4 damage per turn). Yes, I know you can shift attacks off with another Gravity Pull or Armagio, but that's throwing yet another card into the combo.
Marauder + 1-2 BB + GP + (Armagio or GP) + 6-12 turns delay = Massive powerhouse... maybe. As long as the opponent doesn't carry around BB/Auburn Nymph,
or Congeal/Arctic Squid/Permafrost Shield/Ice Bolt,
or Gravity Pull,
or RT/Eternity,
or Mutation/Fallen Druid,
or Gravity Shield or Otyugh,
or Phase Shield/Wings...
or ANTIMATTER/Purple Nymph...
You can get around these with Momentum and Quintessence, but that's adding another element and another two cards, and at that point things just get ridiculous. You could make a 100-HP OTK with that number of cards, and you wouldn't need to wait at least six turns after playing everything to do it.
Also, since you'll be taking off GP when the Marauder's going to die, it's close enough to 0 HP that even damaging CC might take it down.
Because of Reverse Time, the only "buffing" creatures that can feasibly be used are those creatures that don't require a significant card investment to be useful.
I dont consider cards UP by law of RT, becaue I believe RT is widely overpowerd.
Multiple BB do not add onto the delays, it sets the time to 6 so using multiple in 1-2 turns would not be a big deal
Enemy BB is a decent counter but just fuels your creature.
Not sure how Auburn nymph is a counter, Black hole doesnt really stop duos
If you time your GP right, all of the non-bolt damaging CC should not be a problem, nor otyugh
My suggested duo is the very common earth-gravity, so expecting to have momentum, armagion, GP, etc would not be unreasonable
Antimatter is a good counter here, just like it is on most growing creatures, however you're already packin BB so just BB your marauder
Shields block damage, so yeah, effective counters, however this deck likely would pack pulverizers (eart grav duo)
Freeze is an effective counter as with all creatures, and the best counter here
Mutation is a semi-effective counter, though you could always get something awesome.
and speaking of "at least two to 3 more cards to be strong" *cough* shrodingers cat *cough*