If you place a boss on 1st slot you will receive automatically 25% boss loot bonus. The left 175% you must grind through hunting bosses.
Below I'm attaching a table with neccessary boss points to achieve the goal.
| % boss loot bonus | Bosstiary Points |
| 27% | 20 |
| 28% | 30 |
| 29% | 40 |
| 30% | 50 |
| 31% | 60 |
| 32 | 70 |
| 33 | 80 |
| 34 | 90 |
| 35 | 100 |
| 36 | 110 |
| 37 | 120 |
| 38 | 130 |
| 39 | 140 |
| 40 | 150 |
| 41 | 160 |
| 42 | 170 |
| 43 | 180 |
| 44 | 190 |
| 45 | 200 |
| 46 | 210 |
| 47 | 220 |
| 48 | 230 |
| 49 | 240 |
| 50 | 250 |
| 51 | 270 |
| 52 | 290 |
| 53 | 310 |
| 54 | 330 |
| 55 | 350 |
| 56 | 370 |
| 57 | 390 |
| 58 | 410 |
| 59 | 430 |
| 60 | 450 |
| 61 | 470 |
| 62 | 490 |
| 63 | 510 |
| 64 | 530 |
| 65 | 550 |
| 66 | 570 |
| 67 | 590 |
| 68 | 610 |
| 69 | 630 |
| 70 | 650 |
| 71 | 670 |
| 72 | 690 |
| 73 | 710 |
| 74 | 730 |
| 75 | 750 |
| 76 | 770 |
| 77 | 790 |
| 78 | 810 |
| 79 | 830 |
| 80 | 850 |
| 81 | 870 |
| 82 | 890 |
| 83 | 910 |
| 84 | 930 |
| 85 | 950 |
| 86 | 970 |
| 87 | 990 |
| 88 | 1010 |
| 89 | 1030 |
| 90 | 1050 |
| 91 | 1070 |
| 92 | 1090 |
| 93 | 1110 |
| 94 | 1130 |
| 95 | 1150 |
| 96 | 1170 |
| 97 | 1190 |
| 98 | 1210 |
| 99 | 1230 |
| 100 | 1250 |
| 101 | 1275 |
| 102 | 1305 |
| 103 | 1340 |
| 104 | 1380 |
| 105 | 1425 |
| 106 | 1475 |
| 107 | 1530 |
| 108 | 1590 |
| 109 | 1655 |
| 110 | 1725 |
| 111 | 1800 |
| 112 | 1880 |
| 113 | 1965 |
| 114 | 2055 |
| 115 | 2150 |
| 116 | 2250 |
| 117 | 2355 |
| 118 | 2465 |
| 119 | 2580 |
| 120 | 2700 |
| 121 | 2825 |
| 122 | 2955 |
| 123 | 3090 |
| 124 | 3230 |
| 125 | 3375 |
| 126 | 3525 |
| 127 | 3680 |
| 128 | 3840 |
| 129 | 4005 |
| 130 | 4175 |
| 131 | 4350 |
| 132 | 4530 |
| 133 | 4715 |
| 134 | 4905 |
| 135 | 5100 |
| 136 | 5300 |
| 137 | 5505 |
| 138 | 5715 |
| 139 | 5930 |
| 140 | 6150 |
| 141 | 6375 |
| 142 | 6605 |
| 143 | 6840 |
| 144 | 7080 |
| 145 | 7325 |
| 146 | 7575 |
| 147 | 7830 |
| 148 | 8090 |
| 149 | 8355 |
| 150 | 8625 |
| 151 | 8900 |
| 152 | 9180 |
| 153 | 9465 |
| 154 | 9755 |
| 155 | 10050 |
| 156 | 10350 |
| 157 | 10655 |
| 158 | 10965 |
| 159 | 11280 |
| 160 | 11600 |
| 161 | 11925 |
| 162 | 12255 |
| 163 | 12590 |
| 164 | 12930 |
| 165 | 13275 |
| 166 | 13625 |
| 167 | 13980 |
| 168 | 14340 |
| 169 | 14705 |
| 170 | 15075 |
| 171 | 15450 |
| 172 | 15830 |
| 173 | 16215 |
| 174 | 16605 |
| 175 | 17000 |
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