Unless stated otherwise, everything here is Diablo II: Resurrected build 3.3.93847, Reign of the Warlock.
Unless stated otherwise, everything here is Diablo II: Resurrected build 3.3.93847, Reign of the Warlock.

Passive - improves duration and life when in werewolf or werebear form.
Lycanthropy is the Druid's level 1 Shape Shifting passive, requiring Werewolf; it unlocks nothing. The table calls it "Shape Shifting". It has no cast and no mana: it adds duration and maximum life to Werewolf and Werebear while you are in either form. The two numbers are +40 seconds and +20% life at level 1 and +420 seconds and +115% life at level 20.
| Level | Duration: + | Max Life: + |
|---|---|---|
| 1 | 40 seconds | 20% |
| 2 | 60 seconds | 25% |
| 3 | 80 seconds | 30% |
| 4 | 100 seconds | 35% |
| 5 | 120 seconds | 40% |
| 6 | 140 seconds | 45% |
| 7 | 160 seconds | 50% |
| 8 | 180 seconds | 55% |
| 9 | 200 seconds | 60% |
| 10 | 220 seconds | 65% |
| 11 | 240 seconds | 70% |
| 12 | 260 seconds | 75% |
| 13 | 280 seconds | 80% |
| 14 | 300 seconds | 85% |
| 15 | 320 seconds | 90% |
| 16 | 340 seconds | 95% |
| 17 | 360 seconds | 100% |
| 18 | 380 seconds | 105% |
| 19 | 400 seconds | 110% |
| 20 | 420 seconds | 115% |
| 21 | 440 seconds | 120% |
| 22 | 460 seconds | 125% |
| 23 | 480 seconds | 130% |
| 24 | 500 seconds | 135% |
| 25 | 520 seconds | 140% |
| 26 | 540 seconds | 145% |
| 27 | 560 seconds | 150% |
| 28 | 580 seconds | 155% |
| 29 | 600 seconds | 160% |
| 30 | 620 seconds | 165% |
Both lines read lvl, so +skills from items count. The forms read Lycanthropy's lines, not the other way round: Werewolf's and Werebear's duration is 1000 + Shape Shifting.ln12 frames and their life is their own flat percentage plus Shape Shifting.ln34.
The Basin's page records the older values: in the 1.10–1.13 era the lines were 15 + 5 × slvl life and 20 + 20 × slvl seconds, which are the same numbers as today's.
Lycanthropy does nothing in human form. The moment you cast a form, its duration is the form's 40 seconds plus Lycanthropy's seconds, and its life bonus is the form's own flat percentage plus Lycanthropy's: for a wolf 25% + Lycanthropy, for a bear 75% + Lycanthropy, both applied as item_maxhp_percent, the same stat as Increase Maximum Life on gear. The whole is one bonus on your Life.
Because the life is a percentage of your maximum, it grows with everything that raises the base, see Life, Mana and Stamina by Class.
The life bonus ends with the form: dropping to human form, or the form running out, takes it away at once.
No synergies: nothing reads Lycanthropy as a synergy, and it reads nothing. It is itself the term in two other skills' lines, Werewolf's and Werebear's, and both of those read it as lvl, so a +3 Shape Shifting pelt adds 60 seconds and 15% life to the form.
Lycanthropy never touches a player; it lengthens your forms and raises your life in them. See Player versus Player for how your own hits are cut.
Written from the game's tables (build 3.3.93847) and the cited pages; a per-level table is computed from skills.txt and skilldesc.txt by the same evaluator the skill pages use. A “legacy rule” is a published engine rule no table proves; a “game table” is read from the table named. · Report incorrect data