I played the card Desperate Sentry. It died and I put a 3/2 colorless token on the board. My friend then said that it had summoning sickness and wouldn't be able to attack my next turn. I said the summoning sickness would be over when my next turn begins and that it should be able to attack. Who is right?
302.6. A creature's activated ability with the tap symbol or the untap symbol in its activation cost can't be activated unless the creature has been under its controller's control continuously since his or her most recent turn began. A creature can't attack unless it has been under its controller's control continuously since his or her most recent turn began. This rule is informally called the "summoning sickness" rule.
Basically, it can attack/tap if you've controlled it since the beginning of your most recent turn.
When Desperate Sentry dies, the token it makes will be able to attack on "your next turn".
This means right after the next time you untap, etc.
(Barring some card that changes things, obviously, just basically think that your untap step is what removes summoning sickness from all of your creatures)
If the token came in during your own turn, it can't swing yet. Next turn.
If the token came in during your opponents turn, it's good to go as soon as your next turn starts.
You were right. If your creature has been under your control since the beginning of your most recent turn, then its summoning sickness is gone and you can tap it.
You are correct. You can attack with a creature as long as you controlled it continuously since your most recent turn began (C.R. 302.6). If the token entered the battlefield (whether or not it did so on your turn), you can attack with it beginning with your next turn (as long as nothing changes who controls that token in the meantime).
Another newbie question, how do you get the card to pop up like that??
It's called card tags and it's actually mandatory here (no big deal, you didn't know, now you do!) I sent you a private message with the explanation.
-MadMage
For the record, I won anyway
Basically, it can attack/tap if you've controlled it since the beginning of your most recent turn.
When Desperate Sentry dies, the token it makes will be able to attack on "your next turn".
This means right after the next time you untap, etc.
(Barring some card that changes things, obviously, just basically think that your untap step is what removes summoning sickness from all of your creatures)
If the token came in during your own turn, it can't swing yet. Next turn.
If the token came in during your opponents turn, it's good to go as soon as your next turn starts.
No longer staff here.
EDIT (Dec. 22, 2018): Correctness edit.
Another newbie question, how do you get the card to pop up like that??
It's called card tags and it's actually mandatory here (no big deal, you didn't know, now you do!) I sent you a private message with the explanation.
-MadMage
http://www.mtgsalvation.com/forums/magic-fundamentals/magic-rulings/251940-cardtag-explanation-aka-you-must-use-cardtags-in
Former Rules Advisor
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[card]Desperate Sentry[/card] -> Desperate Sentry
No longer staff here.