The defaults below, including the [Rampage], are to be pasted into your GameUserSettings.ini file at the bottom. From there, they can be adjusted.

The default location of this file in your Steam folder for Single Player is
\Steam\steamapps\common\ARK\ShooterGame\Saved\Config\WindowsNoEditor

The default location of this file in your Steam folder for Servers is
\Steam\steamapps\common\ARK\ShooterGame\Saved\Config\WindowsServer
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Defaults:

[Rampage]
BonusStep=0.1
MaximumBonus=2.0
DecayRate=0.05
DecayTimer=3
MaximumHealth=0.25
PlaySound=True
AllowPlayers=True
AllowTames=True
TameWhitelist=
TameBlacklist=
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BonusStep = How much damage is gained per attack.
---Default = 0.1 (10%), Minimum = 0.01 (1%), Maximum = 0.01 (10%).

MaximumBonus = The Maximum damage % during RAMPAGE.
---Default = 2.0 (200%), Minimum = 1.5 (150%), Maximum = 2.5 (250%).

DecayRate = The amount of Damage % you lose per second when not attacking.
---Default = 0.05 (5%), Minimum = 0.01 (1%), Maximum = 0.1 (10%).

DecayTimer = How long after you stop attacking that the Damage % starts falling.
---Default = 3.0 (3 Sec), Minimum = 0.01 (Immediate), Maximum = 5.0 (5 sec).

MaximumHealth = The % Health below which RAMPAGE activates.
---Default = 0.35 (35%), Minimum = 0.1 (10%), Maximum = 0.5 (50%).

PlaySound = Whether or not to play that classic RAMPAGE sound on activation.
---Default = True. Minimum = False, Maximum = True.

AllowPlayers = Whether or not to allow Players to go into RAMPAGE.
---Default = True. Minimum = False, Maximum = True.

AllowTames = Whether or not to allow RIDDEN tames to go into RAMPAGE.
---Default = True. Minimum = False, Maximum = True.

TameBlacklist = Classes of Tames to blacklist from going into RAMPAGE
---You MUST use Dino CLASSES for this, separated by comma (No spaces).
---EXAMPLE: Para_Character_BP_C,Raptor_Character_BP_C

TameWhitelist = Classes of Tames to whitelist for RAMPAGE.
---ONLY these classes will gain RAMPAGE. Recommended left BLANK.
---You MUST use Dino CLASSES for this, separated by comma (No spaces).
---EXAMPLE: Para_Character_BP_C,Raptor_Character_BP_C