This is a basing idea.
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The HeadQuarter would act like a base, and is similar to classic. There are 4-5 rooms a squad must go in to take the flag. Each room would be assigned(by the leader) a few members of the defending squad, and the final guarded by the leader and one other member.
E.G:
Squad A is defending, Squad B is attacking.
A-Leader assigns:
A-1 and A-2 to room one
A-3, A-4 and A-9 to room two
A-5, A-6 and A-7 to room three.
A-8 with himself in the final room.
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If a defending squad member dies, they must wait until all of the attacking squad members die, or the rest of the defending squad members in the room die. The attacking squad members get 5 seconds to advance. If no one is assigned to a room, the attacking squad simply advances to the next room.
EG:
Squad B has 5 members online(active): B-1, B-2, B-3, B-4 and B-Leader.
All of them attack room one. A-1 and A-2 die. Squad B advances to room two, and A-1 and A-2 respawn in their room (they cannot go into a different room unless the leader assigns them to a different room, though they can leave the tower whenever they want)
In room two, A-9 is offline, so only A-3 and A-4 can guard the room. A-3 dies, but A-4 manages to defeat all of Squad B. A-3 respawns in room two and A-4 is healed. Squad B's members decide to wait for everyone to die before attacking again.
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In the final room, the leader and the other member wait. They revive as soon as they die. If the attacking squad manages to secure the headquarter (shoot a block or something 20 times). Then the attacking squad wins.
EG:
Squad B makes it to the final room after a lot of struggle. A-Leader is killed by B-1, and revives. Eventually, Squad B shoots the block 20 times and they win the headquarter.
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Note:
-Once an attacking squad member dies, they cannot enter again until there are only 3 attackers left inside the HQ.
-The (defence) leader can assign a member to a different room, but they must die and respawn in that room, or leave and reenter the HQ at anytime.
-Any player can leave the HQ at any time.
-If the (defence) leader is not online a member may take the leaders place in the final room.
Sorry if this is confusing x.x I'm no good at explaining things.