To double the number of +1/+1 counters on a permanent, put a number of +1/+1 counters on it equal to the number it already has. Other effects that interact with putting counters on it will interact with this effect accordingly.
Delirium — Whenever this creature enters or attacks, if there are four or more card types among cards in your graveyard, distribute two +1/+1 counters among one or two target creatures. Then if there are six or more card types among cards in your graveyard, double the number of +1/+1 counters on those creatures.
