A plugin that can be especially useful if you play as BK (Rathma o Pestilence) to see if you're taking the majority of the damage bonus.
It will be displayed while the boss is alive, if one of the players has the Toxin or IceBlink gems and if there is a player with the full Rathma or Pestilence set.
Currently, the plugin doesn't check that all supports (Zdh and Zbarb) are in the party, nor do they check for skills or items used by players. All icons will be visible, even if they're not relevant.

Funerary Pick (Siphon, rune Power Shift) => If the boss is easily targetable the icon should be permanently bordered in green. The icon texture should actually be that of the FP weapon, I chose the icon of the siphon skill because it triggers the bonus.
Krysbin => You'll be able to see when the highest bonus (300%) is active (it's only actually checked if the boss is Frozen, Stunned, or Blind). The first bonus (100%) will be ignored because it should be permanent when the previous one is not active.
Companion (rune Wolf) => Check the buff on the BK.
Odyssey´s End Bow (Entangling shoot, rune Chain Gang) => The zdh should be constantly renewed, the bonus lasts 2 seconds.
Mark Of The Death (rune Valley of Death) => The Boss must have this Mark permanently if it does not move.
StrongArm => Strongarm Bracers bonus (knockback)
Gem Toxin => Applied when hitting the boss
Gem IceBLink => Multishoot with the cold rune activates this gem.
Download: Plugins\RNN\BossSupportBuffs.cs
Code:
Hud.GetPlugin<RNN.BossSupportBuffs>().Enabled = true;
Hud.RunOnPlugin<RNN.BossSupportBuffs>(plugin =>
{
plugin.Xpor = 0.50f; // Valid values: from 0f to 1f . To set the x coordinate of the center
plugin.Ypor = 0.001f; // Valid values: from 0f to 1f . To set the y coordinate of the center
plugin.Opacity = 0.85f; // 0f..1f Opacity for icon texture
plugin.SizeMultiplier = 0.55f; // Size multiplier for icons
} );