Tetravus

Flying
This creature enters with three +1/+1 counters on it.
At the beginning of your upkeep, you may remove any number of +1/+1 counters from this creature. If you do, create that many 1/1 colorless Tetravite artifact creature tokens. They each have flying and "This token can't be enchanted."
At the beginning of your upkeep, you may exile any number of tokens created with this creature. If you do, put that many +1/+1 counters on this creature.

Doubling Season

If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.
If an effect would put one or more counters on a permanent you control, it puts twice that many of those counters on that permanent instead.

Bellowing Elk

As long as you had another creature enter the battlefield under your control this turn, this creature has trample and indestructible.

Cactuar

Trample
At the beginning of your end step, if this creature didn't enter the battlefield this turn, return it to its owner's hand.